Wash the spinach thoroughly and remove excess water.
Thinly slice the onion and bell pepper.
Add olive oil to a pan and sauté the spinach and vegetables.
Spread tomato sauce on top of the tortilla.
Place the sautéed vegetables on the tortilla.
Sprinkle mozzarella cheese over the top.
Bake the tortilla in a preheated oven or pan until the cheese melts.
Cut into bite-sized pieces.