For the marinade: Combine all ingredients and massage into beef. Cover and refrigerate for a few hours or overnight. Pull out of cooler and bring to room temperature one hour before cooking.
For the relish: Prepare all ingredients and keep separate (mise en place). Just before serving, combine all ingredients and add salt and pepper to taste. To cook the steak: Season the marinated steak with salt and pepper and either char the steaks in a heavy, cast iron skillet or grill over a charcoal fire. Sear over very high heat for 2 to 3 minutes. Turn and lower the heat to medium and cook for 2 to 3 minutes more for medium rare. Remove to a cooling rack and allow to rest for 3 minutes. Slice the steaks across the grain and top with Watermelon relish. Serve with roasted new Potatoes, mashed Sweet Potatoes or grilled sourdough bread and an Arugula salad. Serves 4.
Note: To order Niman Ranch meats, please visit them at www.nimanranch.com.