Chicken Tostadas

Name: Chicken Tostadas
Ingredients: 8 tostadas; 1 cup refried beans, warmed; 4 cups cooked chicken, shredded; 2 cups finely shredded lettuce; 1 medium red onion, thinly sliced into rings; 8 radishes, thinly sliced; 1 cup crumbled queso fresco or mild feta cheese; Mexican sour cream or regular sour cream, for drizzling; Fresh Tomatillo-Avocado Salsa, recipe follows; 8 ounces tomatillos, husked, rinsed and coarsely chopped; 1 avocado, halved, pitted and peeled; 1/2 cup packed fresh cilantro leaves; 1 serrano chile; 1 tablespoon fresh lemon juice; Salt and freshly cracked black pepper