1. heat oven to 350°. mix chili, cumin, salt, pepper, tomatoes in bowl. mix sour cream, scallions, chiles in second bowl.
2. spread 1/2 cup tomato mixture in 13 x 9 x 2-inch baking dish. arrange 2 tortillas to cover bottom; use pieces from another tortilla to fit corners if needed. top with half the sour cream mixture, half the chicken, half the corn, 1 cup tomato mixture, one-third cheese. repeat layering, ending with tortillas, tomatoes. sprinkle remaining cheese around edge.
3. bake in 350° oven 35 minutes, until bubbly. let stand 15 minutes. garnish with olives and scallions.