Prepare the Oven and Dish: Preheat your oven to 400°F. Lightly grease a 13 × 9-inch casserole dish.
Assemble the Base: Spread the spiralized sweet potato evenly in the dish. Add the rinsed rice, mixing slightly to combine.
Mix the Seasoned Liquid: In a large mixing bowl, whisk together the vegetable broth, crushed tomatoes, chili powder, cumin, oregano, garlic powder, salt, and pepper. Add the black beans, corn, diced bell pepper, and onion to the mixture, stirring to combine.
Layer the Ingredients: Pour the seasoned mixture over the sweet potato and rice. Use a spoon to evenly distribute the vegetables and liquid across the dish.
Bake Covered: Cover the dish tightly with aluminum foil or a lid. Bake for 40 to 45 minutes, or until the sweet potato noodles are tender and the rice is cooked through.
Add Cheese and Finish Baking: Remove the lid, sprinkle the grated mozzarella cheese over the top, and bake uncovered for an additional 5 minutes, until the cheese is melted and bubbly.
Garnish and Serve: Let the bake cool slightly. Garnish with avocado slices and freshly chopped cilantro before serving.