Preheat oven to 375°F (190°C).
In a large skillet, heat olive oil over medium heat. Sauté onion and garlic for 2–3 minutes until fragrant.
Add bell pepper and sweet potatoes. Cook for 8–10 minutes, stirring occasionally, until the sweet potatoes begin to soften.
Stir in corn, black beans, diced tomatoes (with juice), cumin, paprika, chili powder, salt, and pepper.
Mix in the cooked rice or quinoa. Simmer for 5 minutes, allowing the flavors to meld.
Remove from heat, stir in lime juice and cilantro (if using).
Transfer the mixture to a lightly greased casserole dish. Spread evenly.
Sprinkle vegan cheese on top (if using).
Bake uncovered for 25–30 minutes, or until bubbly and the top is golden.
Let rest for 5 minutes before serving.