01 - Set your outdoor or stovetop grill to medium-high heat and allow it to reach full temperature before cooking.
02 - Generously brush the tomato halves, onion rings, bell pepper quarters, and garlic cloves with olive oil on all sides using a basting brush.
03 - Place the Italian sausages on the hot grill. Turn occasionally and cook for 12 to 15 minutes until the centers are fully cooked through and the exteriors are nicely charred.
04 - While the sausages cook, grill the oiled tomatoes cut side down, along with the onion, bell pepper, and garlic. Cook for 5 to 7 minutes per side until softened and deeply charred.
05 - Transfer the charred tomatoes, onion, bell pepper, and garlic to a food processor or blender. Add the dried oregano, dried basil, crushed red pepper flakes, and season with salt and black pepper. Pulse until a chunky, rustic sauce forms.
06 - Split each hoagie roll open and place them face-down on the grill for 1 to 2 minutes until the cut surfaces are golden and lightly crisped.
07 - Place a grilled sausage in each toasted roll. Spoon a generous amount of the grilled tomato sauce over each sausage, then sprinkle with shredded mozzarella and grated Parmesan cheese.
08 - Return the assembled grinders to the grill, close the lid, and cook for 2 to 3 minutes until the cheeses are fully melted and bubbling.
09 - Remove from the grill and serve immediately, garnished with fresh basil leaves.