Crab Tostadas with Strawberry-Mango Salsa

Strawberry-Mango Salsa (yield 3 cups):
2 cups fresh strawberries, stemmed and diced
1 cup diced mango
¼ cup thinly sliced green onions
2 Tbsps. chopped cilantro
2 Tbsps. lime juice
1 Tbsp. canola oil.
1-2 serrano chiles, chopped