Prepare the ingredients for the recipe. Depending on the size of the peppers, you might need less or more of them.
In a pan with oil, cook onion with mushrooms until they turn golden brown. Add ground turkey to the mix and continue cooking; stir to break down the meat into small pieces.
To the mixture, add in rice, 1/2 of the sauce and stir to combine it all together. Season to taste.
Stuff each half pepper with the mixture. Combine the rest of the sauce with 2 cups of water and pour it on the bottom of your pan. Place peppers into the sauce, and top each one of them with cheese. Bake at 375°F for 40 minutes.
Serve ground turkey-stuffed bell peppers while they're still hot. They also reheat well.