Pre-heat oven to 350. Place chicken breast in a clear plastic bag. Use a meat mallet to pound until 1/2 inch thick.
Lightly whisk milk and eggs together in a shallow bowl.
Place breadcrumbs in a separate shallow bowl. Stir in Parmesan cheese.
Dip one piece of chicken in egg/milk mixture on both sides, then coat in breadcrumbs.
Place on a parchment paper lined baking tray. Repeat process for remaining pieces of chicken.
Lightly spray chicken with oil. Bake chicken for about 25 minutes.
Remove from oven and spread each chicken breast with tomato sauce. Arrange avocado slices over sauce. Sprinkle with cheese.
Return to the oven and bake another 10 minutes or until chicken is thoroughly cooked.
Serve while hot.