1. In a large skillet, warm 2 Tbsp. oil over medium heat. Add onions, bell peppers and garlic, sprinkle with salt and cook, stirring, until vegetables have softened, 6 to 8 minutes. Remove from heat.
2. Combine beans, cilantro, lime juice, hot sauce, if desired, and 1 Tbsp. olive oil in a medium bowl. Taste and season with salt.
3. Warm a large skillet over medium heat. One at a time, add tortillas and let cook 1 to 2 minutes to soften, flipping once. Spread 1/4 of onion mixture (about 1 cup) along center of each tortilla. Top with bean mixture (about 1/2 cup) and 1/4 of cheese. Fold in sides and roll up tightly. Repeat. Cut burritos in half and serve immediately.