In a large bowl, whisk together the mustard and vinegar, then whisk in 3 tablespoons olive oil. Add the coleslaw mix, season with salt and pepper and toss.
In a large, heavy skillet, heat 1 1/2 tablespoons olive oil over medium-high heat. Add half of the steak in a single layer and cook, turning once, until barely pink, about 2 minutes; transfer to a plate. Repeat with the remaining 1/2 tablespoon olive oil and steak. Return the first batch to the skillet and stir in the barbecue sauce until heated through, 1 to 2 minutes.
Pile the meat onto the roll bottoms and mound some slaw on top. Set the roll tops in place.
