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 using a basting brush, ensuring even coating on all surfaces.
03 - Place the Italian sausages on the hot grill and cook for 12 to 15 minutes, turning occasionally with tongs, until cooked through with a nicely charred exterior and an internal temperature of 160°F.
04 - While the sausages cook, grill the oiled 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 all grilled vegetables to a food processor or blender. Add the dried oregano, dried basil, and crushed red pepper flakes, then 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 crisped.
07 - Place a cooked 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 cheese is fully melted and bubbly.
09 - Remove from the grill, garnish with fresh basil leaves, and serve immediately while hot.