1. Preheat oven to 425ºF. Combine beans, olive oil, scallions, chili powder and 1/2 tsp. salt in a bowl.
2. Mist a baking sheet with cooking spray. Place tortillas on sheet and spoon bean mixture on top. Sprinkle with cheese. Bake until golden and crisp, about 10 minutes.
3. While tostadas are baking, combine mango, onion, lime juice and 1/4 tsp. salt in a bowl. Remove tostadas from oven, spoon mango mixture on top and serve immediately.
Swap salsas. Don't care for mango or can't find one? Sub in tomato salsa instead.
Go green. To add another layer of flavor, sprinkle on some chopped avocado and fresh cilantro after assembling.
Put in more fruit. Mango gives the dish a touch of sweetness. Substitute or add chopped papaya, pineapple or kiwi for even more of a tropical taste.
Try another base. We used small flour tortillas for these tostadas, but you can use corn tortillas if you prefer.