Preheat the oven to 400°F (200°C). Cut the tops off the 4 bell peppers and remove the seeds and membranes; place the peppers upright in a baking dish.
Heat 1 tablespoon olive oil in a medium saucepan over medium-high heat.
Add the chopped yellow onion and sauté, stirring occasionally, for 3–4 minutes until softened and translucent.
Add the 2 minced garlic cloves, chopped green chili pepper (if using), and diced zucchini. Stir in 1 teaspoon ground cumin, 1 teaspoon paprika, 1/2 teaspoon garlic powder, 1/2 teaspoon salt, and 1/2 teaspoon ground black pepper. Cook, stirring, for 5–6 minutes until the vegetables soften.
Add 1 cup dry brown rice, the drained and rinsed 13.5-ounce can of black beans, the 13.5-ounce can of diced tomatoes (with juices), 2 tablespoons tomato paste, and 2 cups of the low sodium vegetable broth. Stir to combine.
Bring the mixture to a gentle boil, then reduce the heat to low, cover, and simmer until the rice is tender and the liquid is absorbed (about 35–45 minutes).
While the rice cooks, keep the prepared bell peppers in the baking dish and reserve 1 cup of the low sodium vegetable broth for baking.
When the rice is done, remove the saucepan from the heat and stir in 3/4 cup of the shredded cheddar cheese until melted and evenly distributed.
Spoon the rice mixture evenly into the prepared bell peppers.
Pour the reserved 1 cup vegetable broth into the bottom of the baking dish around the peppers (not inside them). Cover the dish tightly with foil.
Bake the covered peppers in the preheated 400°F oven for 20 minutes.
Remove the foil, sprinkle the tops of the peppers with the remaining 1/4 cup shredded cheddar cheese, and bake uncovered for an additional 5 minutes, until the cheese is melted and the peppers are tender when pierced with a fork.
Remove from the oven and let the peppers rest for a few minutes before serving.