Prepare the rice according to package instructions.

In a skillet, heat olive oil over medium heat. Sauté onions until translucent, then add garlic and cook for 1 minute.

In a bowl, combine cooked rice, sautéed onions, garlic, zucchini, mushrooms, diced tomatoes, black beans, paprika, cumin, salt, and pepper.

Preheat oven to 375°F (190°C). Cut tops off bell peppers, remove seeds, and place in a baking dish.

Stuff each pepper with the rice mixture and top with cheese if desired.

Cover with foil and bake for 30 minutes. Remove foil and bake for an additional 10-15 minutes.

Garnish with parsley or cilantro before serving.