Preheat a broiler.
Combine the flank steak with the red wine, pineapple juice, soy sauce, red wine vinegar, green onions, tarragon, sage and garlic in a large zip-top plastic bag. Close the bag and let the steak marinate in the refrigerator for 30 minutes. Turn once while marinating. Remove the steak from bag and reserve the marinade.
Place the steak in the broiler, and cook 4-5 minutes on each side until it reaches your desired doneness. Let the steak rest for 5 minutes. Cut the steak across the grain in thin strips.
While steak cooks, combine the reserved marinade, tomato paste, and mustard in a medium saucepan. Place over medium-high heat and bring to a boil, whisking a few times while the mixture heats. Cook for 5-6 minutes, or until the mixture is reduced to 1 cup. Serve the sauce with steak.