Saute the yellow onion, garlic and gr onions in the olive oil just until tender. Remove from the pan and set aside. Remove skins and bones from chicken breasts and pound them flat. Mix flour, salt and pepper together and place in flat bowl. Dip chicken into flour mixture, lightly brown chicken in butter 2 or 3 minutes per side. Add the sauted onions and garlic. Over high heat add sherry, lemon juice and capers. This should thicken to make a nice gravy for chicken.