Preheat the oven to 360°F/180°C.
Prepare the bell peppers by slicing them in halves, then remove the seeds and the membrane. Brush them with a little bit of olive oil inside out, and roast them until they're just undercooked (about 10 minutes).
In a non-stick pan, saute the diced onion until soft and translucent. Then add the ground turkey or chicken, fajita seasoning, salt, and pepper.
Brown the ground meat as you break it down with a wooden spoon, add a can of diced tomatoes, and cook everything together.
Add in cooked rice and mix well, cook for a couple of minutes.
Take the bell peppers out of the oven. They should be roasted but just undercooked.
Spoon the stuffing into each bell pepper half, then top with more mozzarella cheese.
Put back in the oven for 10 minutes. This will allow the flavors to settle, the bell peppers will be fully cooked, and the cheese will melt.