Preheat the oven to 375°F.

Place the thawed frozen spinach in a strainer and press it well to remove all excess water, then transfer it to a cutting board and roughly chop it into pieces.

In a large bowl, add the sour cream, cream cheese, parmesan cheese, onion powder, garlic powder, salt, and black pepper, and whisk to combine. Add the drained, quartered artichoke hearts and spinach and stir until well incorporated.

Place the chicken breasts on a cutting board, season with additional salt and pepper on both sides, and then transfer them to a large 9x13-inch casserole dish.

Pour the spinach artichoke mixture into the baking dish and spread it out evenly to cover the chicken.

Transfer the casserole dish to the oven and bake for 20 minutes. Then remove from the oven, top with shredded mozzarella, and return to the oven for 10-15 minutes until the chicken is cooked through or has reached an internal temperature of 165°F.

Once baked, remove the chicken from the oven and serve immediately on its own or with rice, potatoes, or pasta.