Creating the Baked Tuscan Chicken Casserole is a straightforward process when you follow these steps:

1. Preheat Oven: Preheat your oven to 375°F (190°C) to prepare for baking.
2. Prepare Chicken: Trim and dice the boneless chicken breasts into bite-sized pieces. Season them with salt, pepper, dried basil, and oregano.
3. Sauté Aromatics: In a large skillet, heat olive oil over medium heat. Add chopped onions and cook for 3-4 minutes until softened.
4. Add Garlic: Stir in minced garlic and cook for an additional minute, ensuring it doesn’t burn.
5. Cook Chicken: Add the seasoned chicken to the skillet. Cook for 5-7 minutes until the chicken is browned and cooked through.
6. Combine Ingredients: In a large bowl, mix together the cooked chicken, sun-dried tomatoes, fresh spinach, ricotta cheese, half of the mozzarella cheese, and half of the Parmesan cheese. Add balsamic vinegar and chicken broth for extra flavor and moisture.
7. Transfer to Baking Dish: Spoon the mixture into a greased 9×13 inch baking dish, spreading it evenly.
8. Top with Cheese: Sprinkle the remaining mozzarella and Parmesan cheeses evenly over the top.
9. Bake: Place the casserole in the preheated oven and bake for 30-35 minutes until the cheese is melted and bubbly.
10. Cool & Serve: After baking, let the casserole cool for about 10-15 minutes before serving. This allows the flavors to meld together more perfectly.

By following these simple yet effective steps, you can create a flavorful Baked Tuscan Chicken Casserole that will impress everyone at your table.