1. 1. Saute the Chicken: Heat the olive oil in a large skillet or Dutch oven over medium-high heat. Add the cubed chicken breasts and cook, stirring occasionally, until the chicken is browned on all sides and cooked through, about 5-7 minutes. Once cooked, remove the chicken from the skillet and set it aside on a plate.

2. 2. Build the Aromatic Base: Reduce the heat to medium. Add the chopped yellow onion to the same skillet and cook until it softens and becomes translucent, which usually takes about 3-4 minutes. Then, stir in the minced garlic and cook for another minute until fragrant, being careful not to burn the garlic.

3. 3. Simmer the Sauce: Pour in the diced tomatoes (undrained), tomato sauce, and chicken broth. Stir well to combine all the ingredients. Add the Italian seasoning, salt, and black pepper. Bring the mixture to a gentle simmer, then reduce the heat to low, cover, and let it cook for about 5 minutes to allow the flavors to meld.

4. 4. Add the Tortellini: Uncover the skillet and gently stir in the refrigerated cheese tortellini. Make sure the tortellini is submerged in the sauce as much as possible. Increase the heat slightly to maintain a gentle simmer, cover the skillet again, and cook for 7-9 minutes, or until the tortellini is tender and cooked according to package directions. Stir occasionally to prevent sticking.

5. 5. Incorporate Spinach and Chicken: Once the tortellini is cooked, stir in the fresh spinach a handful at a time. The spinach will wilt down quickly into the hot sauce. Return the cooked chicken to the skillet and stir everything together until the spinach is fully wilted and the chicken is heated through.

6. 6. Finish with Cheese: Remove the skillet from the heat. Sprinkle the 1/2 cup of grated Parmesan cheese over the top of the dish. Stir gently until the cheese is melted and well combined, creating a creamy, cheesy finish. Serve immediately with extra Parmesan cheese on the side.