Preheat oven to 400 degrees.

Spray 15 muffin cups with cooking spray.

In a large bowl, whisk together the flour, baking powder, salt and pepper. Add in the Parmesan, chicken and vegetables. Stir until everything is well coated with the flour mixture.

In a separate bowl, whisk together the buttermilk, melted butter and egg.

Add the buttermilk mixture to the flour mixture. Fold together with a wooden spoon or spatula until no streaks of flour remain.

Scoop muffin batter evenly into prepared muffin cups.

Bake for 17 - 20 minutes, or until a toothpick inserted in the center of a muffin comes out clean.