01 - Set your outdoor or stovetop grill to medium-high heat and allow it to fully preheat.
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, turning occasionally, until cooked through with a nicely charred exterior, about 12 to 15 minutes.
04 - While the sausages cook, grill the tomatoes cut side down along with the onion, bell pepper, and garlic until charred and softened, 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, crushed red pepper flakes, and 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 crisp.
07 - Arrange a grilled sausage on each toasted roll. Spoon a generous amount of the grilled tomato sauce over each sausage and sprinkle with shredded mozzarella and grated Parmesan if desired.
08 - Place the assembled grinders back on 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 if desired, and serve immediately while hot.