01 - Set your outdoor or stovetop grill to medium-high heat and allow it to reach full temperature before cooking.
02 - Brush the tomato halves, onion rings, bell pepper quarters, and garlic cloves generously with olive oil on all sides.
03 - Place the sausages on the hot grill and cook for 12 to 15 minutes, turning occasionally, until fully cooked through with a nicely charred exterior.
04 - While the sausages cook, grill the tomatoes cut side down along with the onion, bell pepper, and garlic for 5 to 7 minutes per side until charred and softened.
05 - Transfer the grilled tomatoes, onion, bell pepper, and garlic to a food processor or blender. Add the dried oregano, dried basil, red pepper flakes, salt, and black pepper. Pulse until a chunky, rustic sauce forms.
06 - Split the hoagie rolls and place them face-down on the grill for 1 to 2 minutes until lightly golden and crisped.
07 - Place a grilled sausage in each toasted roll, spoon a generous amount of the grilled tomato sauce over the top, and sprinkle with shredded mozzarella and grated Parmesan if desired.
08 - Return the assembled grinders to the grill, close the lid, and cook for 2 to 3 minutes until the cheese is fully melted and bubbly.
09 - Remove from the grill, garnish with fresh basil leaves, and serve immediately while hot.