For the meatloaf: Preheat the oven to 350 degrees F. Line a rimmed baking sheet with parchment paper.
Heat the olive oil in a medium skillet over medium heat. Add the garlic, onion, bell pepper and crushed red pepper if using and saute until the vegetables are tender, about 5 minutes. Set aside to cool.
In a large bowl, combine the beef, Parmesan, breadcrumbs, parsley, Worcestershire sauce, garlic salt, kosher salt, pepper, basil, eggs, 1/2 cup of the marinara and the cooled vegetables. Use your hands to mix everything together. Transfer the mixture to the center of the prepared baking sheet and form into a loaf. Coat the meat loaf with the remaining 1/2 cup marinara.
Bake until the meat loaf is firm, 45 minutes to 1 hour (depending on the shape of your loaf). Let set for about 5 minutes before slicing.
For the sandwiches: Butter the rolls and then sprinkle with garlic salt. Transfer to a baking sheet and bake until light golden and toasted, about 5 minutes.
Add a slice of meatloaf to each toasted roll and top with some of the marinara and 3 slices mozzarella. Return to the oven and bake until the cheese is melted, 8 to 10 minutes.