Preheat the oven to 375℉. Spray a medium casserole dish with nonstick spray.
Place the chicken breasts in the prepared casserole dish.
In a medium bowl, stir together the pumpkin, ¾ cup Parmesan, mayonnaise, garlic and onion powder, parsley, salt and a generous sprinkle of freshly ground black pepper. Divide the mixture evenly over the chicken breasts, patting to cover the tops.
Bake for 30 minutes, uncovered. Sprinkle the remaining Parmesan on top of the chicken. Bake an additional 15 minutes, or until the chicken is cooked through and the cheese is melted. Serve immediately.
Notes
If you are preparing this recipe as GLUTEN-FREE, just be sure to use a brand of mayonnaise that is known to be GF.