First things first, get your oven ready by preheating it to 375°F. While it heats up, place a large skillet over medium-high heat and add the olive oil. Once the oil is shimmering, add the ground turkey and cook it until it's browned all over, using a spoon to break it into smaller crumbles.
With the turkey nicely browned, add the chopped onion, minced garlic, Italian seasoning, salt, black pepper, and red pepper flakes to the skillet. Stir everything together and continue cooking for another 3-4 minutes. You’ll know it’s ready when the onion becomes soft and the garlic is fragrant.
Now it's time to build the filling. Pour the marinara sauce into the skillet and add the chopped spinach. Let it simmer for a couple of minutes until the spinach has wilted into the sauce. Remove the skillet from the heat and stir in the cooked brown rice, fresh basil, and parmesan cheese until well combined.
Take your bell pepper halves and generously spoon the turkey and rice mixture into each one. Don't be shy—pack it in there! Arrange the filled peppers snugly in your 9x13 casserole dish. This helps them stand upright and cook evenly without tipping over.
Place the casserole dish into your preheated oven and bake the peppers uncovered for 30-35 minutes. This initial baking time is crucial for softening the peppers and allowing all the delicious flavors in the filling to meld together. The peppers should be tender when pierced with a fork.
Carefully remove the dish from the oven. Sprinkle the shredded mozzarella cheese evenly over the top of each stuffed pepper. Return the dish to the oven and bake for an additional 10 minutes, or until the cheese is melted, bubbly, and just beginning to turn a beautiful golden brown.
Once the cheese is perfectly melted, take the peppers out of the oven. Let them rest for a few minutes before garnishing with a sprinkle of fresh basil and parsley. This adds a final pop of color and freshness. Serve them hot and enjoy every savory bite!