Heat oil in a large skillet over medium heat. Sauté onion and garlic until soft and fragrant (about 3–4 minutes).
Add bell pepper and corn. Cook until they start to blister and soften, about 5 minutes.
Stir in beans, tomato sauce, chili powder, cumin, and paprika. Simmer for 8–10 minutes, until the sauce thickens slightly and flavors mingle.
Season with salt and pepper. If you want it saucier, splash in a bit of water or veggie stock. If you want it smokier, a pinch more paprika does wonders.
Toast tortillas or warm taco shells as directed on the package. Spoon the bean mixture into shells or over bowls. Top with cilantro, avocado, and lime juice.