Combine barbecue sauce, 2 tbsp of the dressing and garlic in sealable freezer bag

Pierce steak all over with fork; add to bag. Refrigerate for 8 to 12 hours.

Pat steak dry with paper towel; season with pepper and kosher salt. Discard marinade. Grill over medium-high heat for 6 to 8 minutes,turning at least twice, for medium-rare doneness 145°F(63°C). Let rest for 10 minutes.

Meanwhile, pan-fry onion in remaining dressing over medium heat, stirring often until soft and golden, about 10 minutes. Serve with thinly sliced steak on baguette. Top with arugula.