Italian Baked Chicken Thighs

Name: Italian Baked Chicken Thighs
Ingredients: 0.5 tablespoon butter; 0.5 cup onion, chopped; 4 ounces Neufchatel cheese, softened; 2 tablespoons chicken broth; 2 tablespoons creamy basil and ricotta pesto (such as Barilla®); 1 tablespoon dry Italian salad dressing mix (such as Good Seasons®); 0.25 teaspoon garlic powder; 0.25 teaspoon black pepper; 0.25 teaspoon Italian seasoning; 0.25 teaspoon red pepper flakes; 3 cups fresh spinach; 1 cup tomatoes, diced; 1 tablespoon chopped fresh basil; 1 pound skinless, boneless chicken thighs; 1 pinch salt and freshly ground black pepper to taste; 3 slices mozzarella cheese