Heat a tablespoon of vegetable oil in a large skillet over medium-high heat and cook onions until soft; 3-4 minutes. Add ground turkey and garlic and cook until meat is no longer pink; about 5 minutes. Drain any liquid and return meat mixture to the pan.
Stir in 1 cup of salsa, taco seasoning and water. Bring to a boil, then cover and reduce heat to low. Simmer for 10-15 minutes or until sauce is thickened and reduced. Stir in rice, black beans and corn. Stir in half of the cheeses until melted.
Meanwhile, prepare the bell peppers. Slice the pepper in half lengthwise, or cut off the tops of the peppers, depending on whether you want them to lay flat or stand up. Remove and discard seeds and membranes; rinse peppers. Arrange in a baking dish and season with salt and pepper. (Note - the size of the baking dish will depend on how you plan to cut the peppers. I recommend slicing them, then fitting them into the pan you think would be the best fit.)
Stuff peppers with the meat mixture. Top each pepper with a spoonful of salsa and remaining cheese.
Carefully pour 1 cup of chicken broth or water around the peppers.
Cover with nonstick foil and bake in the preheated oven for 45 minutes. Uncover and bake for an additional 10 minutes, or until cheese is melted and bubbly and peppers are tender.
Garnish with fresh minced parsley or sliced green onions and serve immediately with a dollop of sour cream if desired.
Prep these peppers ahead of time, store in the fridge and bake when ready!