In a large bowl, mix together ground beef, bread crumbs, ¾ teaspoon salt (reserve the remaining ¾ teaspoon salt), parsley, black pepper, ketchup and egg. Mix until combined and form into 8 meatballs. Refrigerate for at least 15 minutes.

Preheat gas grill to medium high heat.

Toss together the red and green peppers along with the onions and the olive oil in a grill pan or aluminum foil pan. Sprinkle with the remaining ¾ teaspoon salt. Place the pan on the grill and cook covered for about 15 minutes or until vegetables are tender and starting to brown.

While veggies are cooking, place 2 to 3 meatballs on wooden or metal skewers and place on hot grill. Cook covered for about 8 to 10 minutes, turning every few minutes and cook until meatballs are brown and internal temperature reaches 160 degrees.

Remove meatballs from skewers and top each meatball with ½ slice Provolone cheese. Let the cheese melt while meatballs are sitting in with the onions and peppers.

Slice rolls in half and place some onions and peppers on each slider roll half; top with meatballs and more onions and peppers. Top with remaining rolls. Serve with ketchup if desired.