Heat oven to 350°F. Lightly oil 13 x 9 x 2-inch baking dish.
Sprinkle 1/2 cup corn kernels in prepared dish. Tear 6 corn tortillas into 4 or 5 pieces; arrange, overlapping, to cover bottom of dish
Mix salsa and tomatoes in bowl. In another bowl, stir together yogurt, milk and 1/4 teaspoon salt.
Spoon 1 cup salsa mixture over tortillas in dish. Drizzle with 1/2 cup yogurt mixture; sprinkle with olives. Reserve 1/4 cup each corn and beans; sprinkle remaining corn and beans over casserole. Top with chicken, green onion and cilantro. Sprinkle with remaining 1/2 teaspoon salt, the pepper, cumin and oregano. Sprinkle with half the Cheddar; spoon 1/2 cup salsa mixture over top.
Tear remaining tortillas into pieces. Overlap on top to cover. Sprinkle with reserved corn and beans. Spoon on remaining salsa mixture. Drizzle remaining yogurt mixture over top; sprinkle with remaining Cheddar.
Bake, covered, in 350°F oven 25 minutes. Uncover; bake 10 minutes or until hot and lightly browned. Serve with sour cream and radish slices if desired.