Wash hands with soap and water.

Shred the potato and set aside. (It will darken in color, but this will not affect hash.)

Heat 1 tablespoons butter or oil in a medium/large non-stick skillet. Add onion, bell peppers, celery and garlic. Sauté until lightly browned, 5 minutes. Push vegetables to one side of pan. Add remaining butter or oil. Add potatoes and mix with oil to coat them. Mix and combine well with the vegetables. Cook 3 minutes. If potatoes stick, scrape pan vigorously and move contents around pan to spray the bottom with cooking spray.

Mix in chicken, milk, cayenne, salt and pepper. Spread and flatten out the mixture into a thick cake. Use the edge of a pancake turner to cut it into 4 sections. (Or, hash can be broken into rough pieces while cooking.) Cover the pan. Cook until potatoes are tender and hash is lightly browned, 3 to 5 minutes, turning so bottom sides can also brown. (Spray pan with oil spray if necessary while turning hash.)