Preheat oven to 350 degrees. Grease a 3 quart baking dish (or 9x13 baking pan) and set aside.
Pound chicken breasts to 1 inch thickness. If chicken breasts are very large, you can slice in half and use a single chicken breast for two servings. Set aside.
Pour marinara sauce into bottom of pan. Lay chicken breasts on top. Season tops of chicken breasts with salt, garlic powder, and pepper.
Top each chicken breast with 2 teaspoons of pesto, spreading to coat. Top with mozzarella cheese.
Cover and bake for 18-20 minutes, or until chicken is cooked through and juices run clear.
Optional (but highly recommended) - Uncover, turn on broiler, and broil for 2-3 minutes, or until cheese is lightly browned on top. Watch carefully, as food will brown quickly under the broiler.
This dish makes an excellent freezer meal. Prepare in a freezer safe dish, cover tightly with foil, and freeze raw for up to 3 months. Thaw in the refrigerator the night before. Bake as directed above.
*If serving chicken with pasta, add more marinara sauce to pan as needed.