Yield: 4 servings.
3 cloves garlic, finely minced
2 chipotle chiles en adobo, seeded and chopped
½ tsp. adobo sauce from can of chipotle chiles
2 lemons, divided
½ tsp. cumin powder
8 oz. 2% fat strained Greek yogurt
2 mangos, peeled, pitted and diced (about 1½ cup)
6 scallions, thinly sliced (white and light green parts only)
½ cup fresh cilantro leaves, chopped
1 Tbsp. fresh orange juice
1 ripe avocado, diced
1 Tbsp. cumin powder
1 Tbsp. chili powder
to taste, coarse salt and freshly ground black pepper
1 lb. mahi mahi (or other firm white fish, 1½" thick) at room temperature
1 Tbsp. olive oil, divided
4 tostada shells
1 cup shredded lettuce
For cream: Combine garlic, chipotle chiles, adobo sauce, juice from 1 lemon and cumin powder in a food processor. Blend to form a smooth paste. Add yogurt and pulse until toroughly combined. Season with salt and pepper and set aside.
For salsa: Combine mango, scallions, cilantro, orange juice and salt and pepper in a medium bowl. Stir well. Just before serving, gently fold in avocado.
In a small mixing bowl, combine cumin, chili powder and salt and pepper. Brush fish with ½ Tbsp. olive oil and coat with spice mixture. Let stand for 15 minutes.
Lightly brush grill pan or cast iron skillet with remaining olive oil and heat over high flame. Cook fish, turning once, 3 minutes per side for medium rare (or 4½ minutes per side for medium). Remove from heat and slice into ½"-thick pieces.
To assemble tostadas: Arrange shredded lettuce and cubes of fish over tostada on a plate. Top with 3 generous Tbsp. salsa and spoon cream liberally over the salsa. Serve with lemon wedge.