Lightly grease the insert of a 6-quart slow cooker with non-stick spray.
Place the chicken breasts in the bottom of the slow cooker in a single layer.
In a medium bowl, mix the marinara sauce, Italian seasoning, garlic powder, and onion powder together. Pour this mixture evenly over the chicken.
Cover and cook on LOW for 6-7 hours or on HIGH for 3-4 hours, until the chicken is tender and cooked through (internal temperature of 165°F).
About 15 minutes before serving, sprinkle the shredded mozzarella and grated parmesan cheese over the top of the chicken.
Cover again and cook for an additional 10-15 minutes, or until the cheese is fully melted and bubbly.
Garnish with fresh parsley or basil and serve warm.