Preheat oven to 425.
Place tomatoes in a 9×13 pan and drizzle with ½ tablespoon olive oil. Salt and pepper. Toss to coat. Set aside.
Heat remaining 1½ tablespoons oil in a skillet over medium heat. Saute ground chicken, onion until ground chicken is cooked through. Add the garlic and spinach and cook until spinach is wilted. Season with salt and pepper to taste.
In a large mixing bowl, combine ricotta and Parmesan. Add the ground chicken-spinach mixture, stirring to combine thoroughly.
Stuff filling into peppers dividing equally.
Sprinkle with more Parmesan cheese and arrange in the pan with the tomatoes.
Bake uncovered for 25-30 minutes or until lightly browned. Garnish with more Parmesan and fresh parsley if desired.