Warm the tortillas: Heat tortillas in a dry skillet over medium heat for 20–30 seconds per side. Keep them wrapped in a clean towel so they stay soft and pliable.
Sauté the veggies: In a large skillet, heat olive oil over medium.
Add onion and bell pepper with a pinch of salt. Cook 4–5 minutes until softened.
Add beans and spices: Stir in black beans, cumin, and chili powder. Cook 2 minutes, letting the beans warm and pick up flavor.
Fold in spinach and cook until just wilted.
Scramble the eggs: Push the bean mixture to one side of the skillet. Add a small pat of butter or a drizzle of oil if needed. Crack in eggs, season with salt and pepper, and gently scramble until just set.
Mix everything together.
Add cheese and salsa: Remove from heat. Stir in shredded cheese (if using) and 2–3 tablespoons of salsa. Taste and adjust seasoning.
Assemble the burritos: Lay out a warm tortilla.
Spoon 1/4 of the filling in a line across the center. Top with avocado slices and cilantro if you like.
Fold and roll: Fold the sides inward, then roll tightly from the bottom up to seal the filling.
Optional crisping: Place seam-side down in a lightly oiled skillet over medium heat for 1–2 minutes per side to toast and seal.
Serve: Slice in half if desired. Add extra salsa and a squeeze of lime on the side.