Melt butter in large skillet over medium heat.
Add garlic and sliced onions to pan and cook until lightly carmelized.
Remove onion from pan and set aside,
Cook chicken breasts for about 5 minutes on each side.
Add soup and return onions to pan and continue on medium heat for 20-25 minutes.
Remove breasts and place on baking sheet.
Top each with a slice of provolone and broil until melted.
Stir together cornstarch and water to make a slurry and add to pan, stirring until blended.
Return breasts to pan until ready to serve.