Preheat you oven to 350° degrees
Heat a large pan over medium-high heat and add the oil and onion. Cook, stirring frequently, until onion until the onion begins to brown, about 5 minutes.
Add the garlic, chili pepper, and spices and cook for a minute or two longer.
Add the spinach to the pan and stir everything together so that the spinach wilts. This will only take a minute or two. Remove from heat.
Drain the diced tomatoes and cover the bottom of a medium baking dish with the liquid. Place the tomatoes in the large bowl along with the quinoa and beans.
Add the cooked vegetables to the bowl along with the salt and pepper and mix everything together well.
Cut the tops off of the bell peppers and carefully remove the seeds and ribs. Place them upright in the baking dish.
Divide the quinoa mixture between the four peppers.
Cook for 30 to 35 minutes, until the peppers are tender.