Everyone loves a hero and this meatball one is no exception. Traditional meatballs are simmered in a cheesy tomato sauce until full of flavor. To top them off, we quick pickle cauliflower, carrots, celery and bell peppers. The meatballs get spooned into long, soft rolls that have been toasted and smeared with garlic butter, then they are showered with Parmesan and finished with the veggies. This is saucy, crave-able comfort in sandwich form.
For the giardiniera: Combine the vinegar, sugar, fennel seed, red pepper flakes, oregano, 2 teaspoons salt and 1 cup water in a medium saucepan over a medium-high heat and bring to a boil. Reduce the heat to medium. Add the cauliflower and carrots and cook until slightly softened, 3 to 4 minutes. Add the bell pepper and celery and cook until the vegetables are crisp-tender, an additional 2 to 3 minutes.
In a 1-quart mason jar, combine 1/2 cup of the pickling liquid with the olive oil. Strain the vegetables and spices and transfer to the mason jar. Seal and shake to combine. Set aside at room temperature to continue marinating while you make the heroes.
For the meatball heroes: Finely dice 1 of the hoagie rolls into 1/4-inch pieces and put in a large bowl. Pour the milk over it and set aside to soak for 5 minutes.
Add the ground meat, fennel seed, red pepper flakes, oregano, eggs, half of the garlic, 1/2 cup of the Parmesan, a three-finger pinch of salt and a healthy crack of black pepper to the soaked bread and, using clean hands, delicately combine. Using wet hands, roll the meat mixture into fifteen 1 1/2-inch rounds (about 1/4 cup each), place on a rimmed baking sheet and bake until lightly golden and juicy, about 10 minutes. Set aside.
While the meatballs are baking, melt the butter in a small saucepan over medium-low heat. Once melted, add the remaining garlic and cook until fragrant but still pale, 1 to 2 minutes.
Slice the remaining 5 hoagie rolls in half lengthwise down the tops and place on a rimmed baking sheet. If the rolls are very bready, remove some of the insides to create a space for the meatballs to sit. Using a pastry brush or spoon, brush the garlic-butter mixture over the cut sides of the rolls. Bake until the rolls are golden, 4 to 5 minutes.
Add the tomato sauce to a large pot over medium heat. Add 1/2 cup water to the jar of sauce, seal the lid, shake and pour into the pot; this will ensure you get every last drop. Add the meatballs to the tomato sauce, bring to a simmer and cook until the sauce is warm and the meatballs are cooked through, an additional 5 to 7 minutes.
Place 3 meatballs inside of each toasted hoagie roll, top with some steamy sauce, shower with the remaining 1/2 cup grated Parmesan, top with the giardiniera and parsley and enjoy immediately.