Preheat the oven to 375 degrees F. While waiting for it to preheat, peel and chop the sweet potatoes. You want them about 1/2 inch thick coins. Halve the large coins. Place the potatoes on a large sheet pan. Add 1 tablespoon olive oil and 1 and 1/2 teaspoons seasoning mixture (See next step).
Prepare the seasoning mixture: combine the chili powder, garlic powder, onion powder, dried oregano flakes, paprika, ground cumin, and salt + pepper to taste. (I add about 1 teaspoon of each, but add to personal taste preference). Stir together.
Halve the sweet peppers right down the middle and remove the seeds, membranes, and cores. Place in the center of the sheet pan. (You don't want peppers and sweet potatoes overlapping or you'll steam not roast the ingredients so make sure everything has it's own space!) Drizzle remaining 2 tablespoons olive oil over the peppers and add some salt + pepper to each pepper. Place in preheated oven and cook for 25 minutes.
Meanwhile, in a large skillet, cook and break up the extra lean ground beef until no longer pink (about 5-6 minutes). Drain any remaining grease. Add in the garlic and cook until fragrant, about 30 seconds. Add in the tomato sauce, remaining seasoning mix, and the leftover cooked rice. Stir until combined. Reduce the heat to low and allow to simmer until you're ready to stuff the peppers.
Remove the peppers and toss around the sweet potatoes. Add the meat filling to the sweet peppers making sure you use all of it. Place the pan back in the oven and cook for another 10 minutes. Remove. The sweet potatoes and peppers should be crisp tender (If not return to the oven for another 5-10 minutes). Top each pepper with even amounts of cheese and add back to the oven for another 5 minutes or broil on high for 2-3 minutes.
Remove and serve. Add your favorite toppings. We like sour cream, fresh lime, fresh cilantro, and avocados best! Enjoy!