Preheat oven to 350ºF. Line a rimmed baking sheet with foil. In a large skillet over medium heat, cook sausage, stirring to break up chunks, until browned, 4 to 5 minutes. Put in bowl; wipe out skillet.
Warm oil in skillet over medium heat. Add bell peppers and onion and cook, stirring, until peppers are just tender, about 15 minutes. Stir in sausage, tomatoes, tomato sauce, corn, garlic powder, salt and pepper. Turn heat to high and bring to a boil, stirring occasionally. Reduce heat to medium-low; simmer 10 minutes, stirring once. Add rice.
Pour mixture into a 9-by-13-inch baking sheet. Bake until bubbly, about 30 minutes. Remove from oven; sprinkle with Cheddar. Return to oven; bake until cheese melts, 3 to 5 minutes longer. Let stand 5 minutes before serving.