For the POM Marinated Steak: In a container or zip-top bag, combine the ¾ cup of POM Juice, salt, garlic, mustard, and flank steak. Seal and refrigerate for 1 to 4 hours. Remove from refrigerator 30 minutes before cooking.
For the Swicy POM Sauce: In a saucepan over medium-high heat, bring 1 cup of POM Juice to a simmer. Cook until the juice is reduced by half and remove from heat. Transfer to a bowl and combine with the brown sugar, chili sauce, ketchup, vinegar, Worcestershire sauce, and dry seasonings. Whisk until completely combined.
For the Sheet Pan Dinner: Place the potatoes in a large pot filled with salted, cold water. Cover and boil until the potatoes are tender, about 12 to 15 minutes. Drain and set aside.
Turn the broiler on high and adjust the oven rack to the position closest to the broiler. Line a rimmed baking sheet with foil and place the steak on the sheet pan—discarding the marinade—and broil until the top browns slightly, about 5 minutes.
Gently toss the potatoes, green beans, olive oil, salt, and pepper. Remove the steak from the broiler and add the potatoes and green beans to the pan. Broil until the steak is 140ºF to 145ºF on a meat thermometer (for medium rare) and the veggies are cooked, about 8 to 10 minutes. Use tongs to move the vegetables around to cook evenly.
Generously coat the steak with the Swicy POM Sauce and slice it. Serve with extra sauce for the vegetables. Garnish with POM Arils and parsley.
