Wipe steaks with damp paper towel, sprinkle with salt and pepper. Set aside. In a large frying pan, sauté garlic in butter. Add lemon juice. Add steaks and turn periodically. Cook 4 to 5 minutes or until fish flakes when tested with a fork. Remove steaks to clean platter. Set steaks aside. Sauté mushrooms in butter in same pan. Add chicken stock, cornstarch and soy sauce. Cook, stirring continuously, until sauce thickens. Pour sauce over swordfish steaks.