Preheat the oven to 375F. Add bell peppers to a 9x13-inch baking dish (cut-side-up). Add about 1/4 cup water to the baking dish to help the peppers steam.
In a large skillet over medium heat, warm the olive oil. Add the turkey and ½ teaspoon salt and cook, breaking it up into chunks as it cooks, for about 3-5 minutes or until mostly cooked through.
Add the garlic, oregano, cherry tomatoes, tomato paste, and ½ teaspoon salt and cook for about 3 more minutes or until the tomatoes soften and release their juices.
Stir in the spinach, quinoa, and remaining ½ teaspoon salt. Remove from heat.
Add a spoonful of the ricotta to the bottom of each bell pepper and spread it around the bottom. Top with a sprinkle of cheese. Divide the turkey quinoa mixture between the bell pepper halves, pressing down to pack it in.
Cover with foil and bake for 15 minutes or until the bell peppers are tender. Remove foil and top each bell pepper with another spoonful of remaining ricotta and gently spread it on top and then top with remaining mozzarella cheese. Bake uncovered for 5-10 more minutes, or until the cheese is melted.
Serve warm topped with fresh herbs (if using).