Preheat oven to 350 degrees. Place chicken breasts in a baking pan that has been sprayed with vegetable cooking spray. Bake for 20 to 25 minutes. In the meantime, stir together ketchup, Worcestershire sauce, agave nectar and chili powder to make the barbecue sauce. Remove chicken breasts from oven and coat with sauce. Return to oven and bake for 10 more minutes.