1. In a small bowl, combine the red onion, chopped cilantro, and lime juice. Set aside to marinate, stirring occasionally.
2. In a large heavy skillet, heat ¼-inch of oil over medium heat. Working with one tortilla at a time, spread 1 heaping tablespoon of refried black beans and 1/2 tablespoon of the onion, cilantro, and lime mixture evenly along one side of the tortilla. Gently roll the tortilla tightly beginning on the side with the filling. Use a toothpick to secure the flauta so it doesn't unroll while cooking. (Corn tortillas have a tendency to dry out quickly and split, so I rolled 4 flautas then placed them in the hot pan and rolled 4 more while the others were cooking until they were all finished.)
3. Place the prepared flautas seam side down in the hot oil and cook, rotating with tongs, until they are golden brown and crispy on all sides, approximately 4-5 minutes per batch. Continue to cook the rest of the flautas in batches, adding more oil as needed. Remove the toothpicks after you have fried them and serve with Avocado Dipping Sauce, lettuce, cilantro, cheese, hot sauce, and lime wedges.

Corn tortillas will often tear if they're not warmed before you roll them. To heat them up, simply wrap them in a damp paper towel and heat them in the microwave for 30-45 seconds at a time until they're pliable.

If you'd prefer to bake your flautas, soak the toothpicks in water while you're doing the prep work and preheat your oven to 400ºF. Spray a baking sheet with an oil mister. Prepare the flautas as described in the recipe, then place them on the baking sheet. Spray them with oil and bake for 15-20 minutes, until crisp.