Set the red pepper, onion and garlic on a double layer of foil.
Drizzle with 1 tablespoons of the olive oil and balsamic vinegar and sprinkle with 1/8 teaspoons each of salt and pepper.
Seal foil tightly into a packet.
Set on the grill and cook with the lid closed 8-10 minutes.
Drizzle the steaks with the remaining olive oil.
Grill for 2-3 minutes per side for medium (160F on an instant read thermometer).
Season sreaks with remaining salt and pepper.
Let rest 5-10 minutes.
Meanwhile, mix the chopped arugula into the red pepper, and onion mixture to make a warm relish, seasoning to taste.
Thinly slice the steak and serve topped with the relish.
NO BBQ?
In a roasting pan, combine the red pepper, onion, and garlic with 1 tablespoons olive oil, the vinegar and 1/8 teaspoons salt and pepper, Set the pan in the top third of the oven and broil for 10-12 minutes or until vegetables are caramelized, stirring occasionally.
On the stovetop, sear oiled steaks in an ovenproof skillet over medium-high heat 1 minute on each side.
Transfer the skillet to the oven and broil for 2-3 minutes per side for medium.