1. Place half the beans into a medium bowl. Coarsely mash the beans with a fork. Stir the mashed beans, remaining beans, 2/3 cup picante sauce and onions in a 2-quart saucepan. Cook over medium heat until the mixture is hot and bubbling.
2. Spread the bean mixture on the tostadas or spoon over the tortilla chips. Top with the lettuce, cheese and tomato. Serve with the remaining picante sauce.
Ingredient Note: To make your own tostada shells, heat oil in a 12-inch skillet over medium-high heat. Add 8 corn tortillas in batches and cook until they're crisp. Drain the tostadas on paper towels.
For baked tostada shells, heat the oven to 450°F. Place 8 corn tortillas onto 2 baking sheets. Spray the tortillas with vegetable cooking spray. Bake for 5 minutes or until the tortillas are crisp.
Easy Substitution: You can also serve the bean mixture over tortilla chips.