Place chicken between 2 sheets of heavy-duty plastic wrap; pound to 1/4-inch thickness, using a meat mallet or rolling pin.
Combine ricotta cheese and next 3 ingredients in a bowl. Place 1 slice prosciutto on top of each chicken breast half. Spoon cheese mixture evenly over prosciutto, spreading to 1/4 inch from sides. Roll up chicken, jelly roll fashion; start with short side. Secure with wooden picks.
Place chicken rolls in a 13 x 9-inch baking dish coated with cooking spray. Spoon 1 cup marinara sauce over chicken. Cover and bake at 350° for 15 minutes. Uncover; spoon liquid from bottom of dish over chicken, and bake an additional 5 minutes or until chicken is done. Slice each roll into 4 or 5 slices. Place slices on individual serving plates. Microwave remaining 3/4 cup marinara sauce at HIGH until thoroughly heated. Spoon marinara sauce evenly over slices.