Chicken Taco Casserole

Name: Chicken Taco Casserole
Ingredients: 4 cups shredded chicken; 1 ( 4 - ounce ) can mild green chiles; 2 (1- ounce ) packets taco seasoning , divided; 1 pound shredded colby jack cheese , divided; 2 tablespoons olive oil; 1 medium yellow onion , diced; 1/2 teaspoon kosher salt; 1 1/2 cups corn kernels (no need to thaw if frozen); 1 ( 15 - ounce ) can black beans, drained and rinsed; 1 ( 14 - ounce ) can fire-roasted diced tomatoes; 12 (6-inch) corn tortillas; 8 crispy tostadas; Sour cream , for serving; Chopped cilantro , for serving