Preheat the oven to 375 degrees Fahrenheit.

Place the thawed, frozen spinach in a colander and squeeze out any excess water before transferring to a cutting board and coarsely chopping it into pieces.

Whisk together the sour cream, cream cheese, parmesan cheese, onion powder, garlic powder, salt, and black pepper in a large mixing bowl. Stir in the drained, quartered artichoke hearts and spinach until thoroughly combined.

Place the chicken breasts on a chopping board and season with salt and pepper on both sides before placing them in a large 913-inch casserole dish.

Spread the spinach artichoke mixture equally in the baking dish to cover the chicken.

Bake for 20 minutes, then remove from the oven, sprinkle with shredded mozzarella, and bake for another 10-15 minutes, or until the chicken is cooked through or has achieved an internal temperature of 165°F.

Remove the chicken from the oven and serve immediately, either alone or with rice, potatoes, or pasta. Any leftover chicken casserole may be refrigerated for up to 5 days or frozen for up to 3 months.