Skirt Steak. This cut is part of the diaphragm muscle that lies between the chest and the abdomen. It is a flat, long piece of meat that is very flavorful, but can be tough if it is not marinated or not properly cooked. For a delicious, tender skirt steak: First, marinate in 3 parts olive oil to 1 part acid (wine, vinegar, lemon or lime), and fresh herbs, kosher salt and fresh cracked pepper. Then, on very high-heat; grill, sauté, stir-fry or sear. Serve.