Step 1: Make Meatballs

1. In a large mixing bowl, combine ground turkey or chicken, panko breadcrumbs, egg, minced garlic, Italian seasoning, red pepper flakes, and salt.
2. Mix the ingredients thoroughly, ensuring the spices are evenly distributed.
3. Form the mixture into 24 evenly-sized meatballs.
4. Heat olive oil in a skillet over medium-high heat.
5. Add the meatballs to the skillet, browning them on all sides by turning occasionally.
6. Once the meatballs are browned, reduce the heat to medium-low.
7. Pour in the marinara sauce, cover the skillet, and cook for about 15 minutes until the meatballs are cooked through.

Step 2: Using Frozen Meatballs

1. Begin by heating the marinara sauce in a skillet over medium heat.
2. Add the frozen meatballs to the sauce.
3. Cover the skillet and cook until the meatballs are thoroughly warmed, about 25 minutes.

Step 3: Assemble the Subs

1. Preheat the broiler on your oven.
2. Place the hot dog buns on a baking sheet.
3. Fill each bun with three meatballs.
4. Spoon additional marinara sauce over the meatballs.
5. Sprinkle mozzarella cheese generously on top.
6. Broil for 2-3 minutes, watching closely to prevent the cheese from burning.