(CNN) -- If the first thing that comes to mind when you think of a taco is that crispy corn shell filled with seasoned ground beef, strings of bright yellow cheese and shredded lettuce, then it's time to think beyond the emoji.

October 4 is National Taco Day, but any day in October (or any month, really) is a worthwhile opportunity to dive into the diverse world of tacos.

"When I was living in Mexico, I realized there is this word, 'taquear,' which means to taco something or to go have tacos somewhere," said Lesley Téllez, a New York-based writer and author of "Eat Mexico."

"It's not just a physical thing, it's a way to eat something," she added.

If you have tortillas, you're already halfway to making tacos. Whether built from soft flour or corn (masa) tortillas, fried corn tortilla shells, or other grain variations like quinoa flour or cassava flour tortillas, the taco is really flexible -- both literally and metaphorically. You can buy a stack of ready-made tortillas or make your own at home; King Arthur Baking has a number of recipes using a variety of flours.

Tortillas have been used as edible vessels since the days of the Aztecs, but the popularity of tacos grew with the dispersion of modern Mexican cuisine in the 20th century. They can be stuffed with almost any filling(s) you can imagine: From the puffy tacos of Tex-Mex cuisine to the fish tacos of Baja to food trucks slinging regional specialties, the taco contains multitudes.

And with so many ways to fill a taco, why restrict yourself? "I object to the idea of a taco night because it's not a night -- it can be every day," Téllez said. "There's a whole universe of tacos out there."

This month, use the taco as a canvas for indulging in both traditional and improvised recipes. And if you're anywhere near San Bernardino, California, stop by Mitla Café and try the tacos that inspired the founder of Taco Bell.

Once you've crunched into one of Mitla's freshly fried taco shells -- as I have at the end of a long Route 66 road trip -- you'll wonder how you can ever eat a fast-food taco again.

Hearty meat tacos

When it comes to taco fillings, tender pork and beef are traditional and beloved by many. No doubt you have a favorite taqueria that dishes up a mouthwatering taco platter, but if you want to make your own at home, try these recipes.

Carnitas, made with pork shoulder braised in orange juice and Coca-Cola, are simultaneously juicy and crispy. Traditionally the pork is fried in lard before slow cooking, but this slow cooker carnitas recipe offers the option of using coconut oil.

Barbacoa translates to "barbecue" in Spanish and refers to the method of slow-roasting tough cuts of beef -- or goat or lamb -- in a pit. (When it comes to tacos, beef is typically the most popular meat.) But instead of digging a pit in the backyard, Instant Pot barbacoa makes the process much easier.

Chicken tinga, a Pueblan dish characterized by its spicy chipotle-and-tomato sauce, is another favorite taco filling. This saucy shredded chicken is another taco filling that's easy to replicate in the Instant Pot -- or for a no-stress dinner, use shredded rotisserie chicken.

Vegetarian tacos

For farm-share subscribers who struggle with what to do with their regular produce boxes, tacos are always the answer. If a vegetable can be cooked, it can be turned into a taco filling, according to Tellez. "You can 'taco' a pile of sauteed mushrooms, sauteed squash and chopped tomatoes," she suggested.

Mushroom tacos can be made simply with a skillet of sautéed cremini mushrooms -- or with meaty wild varieties such as oyster mushrooms for a vegetarian version of carnitas. (If you want even more ways to cook with mushrooms, try these ideas.)

Squash tacos can be filled with summer squash and zucchini when those vegetables are in season, or hard squash varieties, such as butternut, kabocha or delicata, during colder months. When delicate squash blossoms are available, grab a handful to pan-fry in a light batter as a fleetingly special taco filling.

In one of Téllez' "Eat Mexico" recipes, shredded carrots make the most unexpectedly delicious taco fillings. They can be rolled in tortillas and pan-fried for a taquito-style meal or simply spooned into a soft tortilla of your choice.

Breakfast tacos for any time of day

Austin, Texas, seems to have single-handedly made the breakfast taco a dish worth waking up for, but you don't need to travel to the Lone Star State -- or anywhere further than your kitchen -- for a loaded-up, fill-you-up tortilla.

Eggs are a standard in breakfast tacos, whether scrambled or fried, but beyond that, it's up to your cravings to dictate what else is included. Chorizo, potatoes, cheese, salsa, beans, avocado (fresh or fried), and even steak or brisket are on the table.

And if all else fails, just look to what you have on hand and turn it into a taco. "My favorite tacos (use) the leftovers that I pull out of my fridge and reinvent," Téllez said.

Her secret for transforming sad leftovers is by always stocking the refrigerator with classic taco toppings that bring big flavor. "I tend to keep a lot of toppings," she explained. "I always keep hot sauce that I love, cilantro, raw jalapeño, and raw cabbage because it stays good forever."

With an arsenal of fresh, spicy and crunchy toppings, everything from fried rice to chopped-up frittatas can become taco fillings. Take stock of what you've got and taquear to your heart's content.

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