Prepare the grill pan and let it get smoking hot. Pour a tablespoon of the olive oil on one side of the meat and rub in. Season with salt and pepper to taste. Sprinkle half of the oregano on top and lightly press into meat. Flip and repeat process on the other side. Grill, turning once, for about 10 minutes or until done to your taste. Let rest for a few minutes before serving.
While steak is cooking, heat the remaining oil until hot in a large saute pan. Add the garlic and saute about 1 minute, or until light brown. Add the greens and toss occasionally. After about 3 minutes the greens will have cooked down. Season with a large pinch of salt and cook another 3 minutes. Transfer to a bowl and let cool. Splash with vinegar to taste.
Cut the flank steak across the grain into 1/4-inch slices. Serve with the greens and finish with drizzle of hot sauce, as desired.