Combine all of the Italian Herb Oil ingredients together in a small bowl. Set aside at room temperature until ready to use.
Toss red onion, zucchini, and bell peppers in olive oil until coated. Season with salt and pepper.
Add vegetables to a hot grill or cast iron grill and cook until caramelized and tender. Takes about 5 minutes on each side. Take off of the grill.
To assemble your sandwich start by smearing the Italian herb oil on the inside of each Hoagie Roll.
Next layer each sandwich with grilled vegetables and top with sliced mozzarella. Place on back of grill and cook until cheese has melted 2-3 minutes on each side. Weigh the sandwich down with a cast iron skillet or a brick covered in aluminum foil. You can also use a cast iron burger press.
Serve and enjoy!
Recipe adapted from: chefsavvy.com.