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, ensuring even coverage for optimal charring.
03 - Place the sausages on the hot grill and cook, turning occasionally with tongs, until cooked through and charred on all sides, 12 to 15 minutes.
04 - While the sausages cook, grill the tomatoes cut side down along with the onion, bell pepper, and garlic until softened and well charred, about 5 to 7 minutes per side.
05 - Transfer the grilled tomatoes, onion, bell pepper, and garlic to a food processor or blender. Add the dried oregano, dried basil, and red pepper flakes, then season with salt and black pepper. Pulse until a chunky, rustic sauce forms.
06 - Split the hoagie rolls and place them face-down on the grill. Toast for 1 to 2 minutes until golden and lightly crisped.
07 - Arrange the grilled sausages in the toasted rolls. Spoon a generous amount of the grilled tomato sauce over each sausage, then sprinkle with shredded mozzarella and grated Parmesan.
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 bubbly.
09 - Remove from the grill, garnish with fresh basil leaves, and serve immediately while hot.