Saute onions, garlic and scallions in olive oil until tender. Remove from pan and set aside. Remove skins and bones from chicken and pound flat. Mix flour, salt and pepper and place in a flat bowl. Dip chicken pieces into flour and lightly brown them in butter, 2-3 minutes per side. Add sauteed onions and garlic. Over high heat, add sherry, lemon juice and capers. This should thicken to make a nice gravy for the chicken. If gravy becomes too thick, add some chicken stock.