1. Place a baking sheet inside oven, and preheat oven to 350°.
2. Lightly coat corn tortillas on both sides with cooking spray; place on preheated pan. Bake at 350° for 6 to 8 minutes or until crisp and golden. Cool tortillas on a wire rack.
3. Heat beans in a small saucepan over low heat 5 minutes, stirring often. Combine lettuce, onions, and cilantro in a bowl; toss.
4. Divide beans evenly among tortillas. Top each tostada with 1/2 cup lettuce mixture, 4 teaspoons cheese, 3 bell pepper rings, 2 avocado slices, 2 tablespoons pico de gallo, 1 tablespoon sour cream, and 1 1/2 teaspoons pepitas. Garnish with lime wedges, if desired.