In a large mixing bowl, combine all the ingredients for the meatballs except for the vegetable oil and marinara/spaghetti sauce. Using your hands, mix the ingredients until just combined. Be careful not to overmix or over-squeeze, as this can result in dense meatballs. Form the mixture into 16 meatballs (about 1 inch in diameter).

Heat the oil in a large skillet (such as a high-sided 12-inch skillet or cast iron) over medium-high heat until shimmering. Carefully add the meatballs to the hot skillet in batches, ensuring you do not to overcrowd the pan. Sear for 2 to 3 minutes per side until they develop a golden-brown crust. Remove the seared meatballs from the skillet, set them aside, and repeat with any remaining meatballs. Wipe down the skillet if you plan to use it for the sauce.

In a saucepan or the cleaned skillet, warm the marinara or spaghetti sauce over medium heat. Once the sauce begins to lightly simmer, gently add the seared meatballs to the sauce. Reduce the heat to low. Cover and simmer until the meatballs are fully cooked to an internal temperature of 160 to 165°F, about 10 to 12 minutes. Season with salt and pepper to taste.

Preheat the oven to 350°F (175°C).

Carefully cut each hoagie roll lengthwise, butterflying it open but being careful not to slice all the way through. Place the rolls cut-side up on a baking sheet. Brush the inside of the rolls with extra-virgin olive oil and bake for about 5 minutes, or until the rolls are lightly toasted. This creates a protective barrier against sogginess and adds a slightly crispy texture.

Preheat the broiler to high.

Spoon a generous amount of meatballs and sauce onto the bottom half of each toasted hoagie roll. Top with 2 slices of provolone cheese followed by the black olives, green bell peppers, and red onions, as desired.

Return the assembled sandwiches (open-faced) to the baking sheet and place them under the broiler until the cheese is melted and bubbly, about 2 to 3 minutes. Watch closely to prevent burning.

Remove from the oven, let cool slightly, and serve immediately.