For the Chamoy Sauce, place all ingredients in blender container; cover. Blend on medium speed until smooth. Set aside.
For the Corn Relish, grill corn over medium heat 10 to 12 minutes or until tender and lightly charred, turning occasionally. Cut corn kernels from cobs. Toss corn with tomatoes, bell pepper, onion, blood orange juice and 1/2 cup of the Chamoy Sauce in large bowl. Refrigerate until ready to serve.
Preheat oven to 350°F. For the Salmon Tostada, place salmon in baking dish. Brush top of each fillet with 1 tablespoon of the remaining Chamoy Sauce. Bake 12 to 15 minutes or until fish flakes easily with a fork. Flake each salmon fillet into large pieces.
To assemble tostadas, place 4 avocado slices in each shell. Top each with about 1/4 cup of the corn relish, 2 tablespoon of the sour cream and flakes from 1/2 of a salmon fillet. Drizzle with remaining Chamoy Sauce.