Preheat oven to 375ºF. Coat a 2-quart rectangular, round or oval baking dish with cooking spray
In a large bowl, combine rice, salsa and cumin. Spoon 2 cups of rice mixture into prepared baking dish and spread out to evenly cover bottom of dish.
In another large bowl, combine refried beans, corn, peppers and chili power. Using a rubber spatula, scrape bean mixture on top of rice layer and smooth out top.
Squeeze out any excess water from spinach and then spread on top of bean layer; sprinkle with 6 tablespoons of cheese. Top with remaining rice mixture and smooth out top; sprinkle with remaining cheese.
Place casserole on a large rimmed baking sheet to catch any spillage. Bake until heated through and cheese is browned and bubbling, about 30 minutes. Cut into 6 pieces and serve.