A grill basket makes easy work of preparing these satisfying sausage sandwiches. A little sweetness from balsamic vinegar and a dose of heat from the serrano pepper take the flavors to the next level. We brush the buns with herbed oil before stuffing them to the brim and digging in.
Mix the balsamic vinegar, garlic, 1/2 teaspoon Italian seasoning, 1/2 teaspoon salt and a few grinds of black pepper in a large bowl. Whisking constantly, slowly drizzle in 2 tablespoons olive oil until emulsified. Add the red pepper, green pepper, serrano pepper, onion, 1/2 teaspoon salt and a few grinds of black pepper and toss until well combined.
Place the basket on a baking sheet and transfer the peppers and onions to the center, letting any extra marinade drip off. Place 3 links of sausage on either side of the veggies. Close and secure the basket.
Place the grill basket on the grill and cook, flipping once, until the vegetables and sausages start to brown and caramelize and an instant read thermometer inserted into a sausage measures 160 degrees F, 10 to 12 minutes.
Meanwhile, mix the remaining 3 tablespoons oil, remaining 1 teaspoon Italian seasoning, 1/4 teaspoon salt and a few grinds of black pepper in a small bowl. Open the hoagie rolls and brush the insides with the herb oil. Grill until toasted, about 1 minute.
Remove to a platter and place 2 overlapping slices provolone on each roll (do not allow cheese to hang over the sides). Return the rolls to the grill, cover, and cook until the cheese is melted, about 1 minute. Remove to a platter.
Remove the peppers and onions from the basket and slice thinly. Cut each link of sausage in half on a deep bias and place in a hoagie roll. Divide the peppers and onions among the rolls and spoon 2 tablespoons warm marinara on top. Serve the hoagies with the remaining marinara on the side for dipping.