Preheat your oven to 400°F.
In a small bowl, mix together the Italian seasoning, onion powder, and garlic powder. Season both sides of the chicken with the seasoning mixture, along with salt and pepper.
Heat an oven-safe skillet over medium-high heat and lightly coat it with avocado oil. Add the chicken and sear for about 3 minutes per side. The chicken does not need to be fully cooked yet. Transfer it to a plate and set aside.
Reduce the heat to medium-low. Add the garlic and spinach to the same skillet and sauté for 2-3 minutes, until the spinach has wilted and the garlic is fragrant.
Pour in the chicken stock, scraping up any browned bits from the bottom of the pan. Let it simmer for about 3 minutes, or until the liquid has reduced by about half.
Stir in the diced tomatoes, half and half, Parmesan cheese, and red pepper flakes. Cook for another 2-3 minutes, stirring occasionally, until the cheese has melted and the sauce is smooth.
Return the chicken to the skillet, spooning some of the sauce over the top. Transfer the skillet to the oven and bake for 10-12 minutes, or until the chicken reaches an internal temperature of 165°F.
Top with freshly chopped parsley and additional Parmesan cheese before serving. Serve with your favorite pasta, rice, or vegetables.