Boil three cups of water. Thinly slice red onion and place in strainer in the sink. In a medium-sized bowl, whisk together 1/4 tsp salt and 1 cup red wine vinegar. Once water comes to a boil, gently pour over onions, as this all lightly cook them. Transfer onions to red wine vinegar and salt mixture. Let sit for a half hour at room temperature. All of the onions don’t need to be covered with vinegar; fold them into the liquid with spatula or spoon about every 10 minutes. Drain after 30 minutes and refrigerate any leftover onion. It will keep for about 2 weeks.
Preheat oven to 350F.
In a pot large enough to fit entire package of vegan meatballs without crowding them, heat to medium high drizzle with olive oil, and add meatballs. Add 3/4 – 1 jar of marinara, turn heat to medium and cover until meatballs are cooked all the way through, about 15 minutes. Gently stir occasionally.
If hoagies are not already cut, slice in half, lengthwise. Thinly slice Miyoko’s Fresh Mozzarella, and even distribute among the four top halves of your bread. Toast all bread, until mozzarella is melted and bread is lightly browned, about 7 – 10 minutes
Remove from oven, let cook slightly. Place a layer of pickled onion on the bottom halves, followed by 3/4 cup arugula each, and then ladle marinara and approximately 3 meatballs on top of arugula. Place top half of bread with melted cheese atop and enjoy!