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 to ensure even charring.
03 - Place the Italian 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 throughout.
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 open and place them face-down on the grill for 1 to 2 minutes until golden and lightly crisp.
07 - Arrange a grilled sausage in each toasted roll and spoon a generous amount of the grilled tomato sauce over the top. Sprinkle with shredded mozzarella and grated Parmesan cheese.
08 - Place the assembled grinders back on 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, garnish with fresh basil leaves, and serve immediately while hot.