Broccolini Cheesesteaks

large carrots, peeled, thinly sliced

bell peppers, ribs and seeds removed, chopped

large white onion, chopped

crushed red pepper flakes

plus 3 Tbsp. extra-virgin olive oil, divided

bunches broccolini, trimmed (about 2 lb.)

garlic cloves, thinly sliced

Kosher salt

plus 2 tsp. sherry vinegar

seeded hoagie rolls (about 8" each)

slices provolone cheese