Preheat the oven to 350 degrees F.
Toss the green and red peppers with the olive oil, granulated garlic and sprinkle with salt and pepper. Lay the peppers on a baking sheet and bake, stirring halfway through, until lighter in color and soft, about 25 minutes. Reserve and don't drain excess oil from the baking sheet.
Meanwhile, preheat a grill or grill pan to medium-high heat. Grill the sausages, covered with a bowl, until nice and charred and no longer pink on the inside, flipping once, about 12 minutes each side.
Preheat the broiler and set the rack to the middle of the oven. Brush the inside of the rolls with the reserved sweet pepper oil from the baking sheet. Place the sausages, peppers, some more of the sweet pepper oil and some of the Homemade Hot Giardiniera on the rolls. Top with the mozzarella and place under the broiler until melty and gooey! Take off your shirt, get some color and eat.
Combine 2 cups water and the salt in a glass or nonreactive bowl. Mix until the salt is dissolved. Add the carrots, cauliflower, serranos, minced garlic, celery and bell peppers to the salt water and stir to combine. Cover and refrigerate overnight.
On day 2, drain and rinse the vegetables. Mix the canola oil, oregano and black pepper in a clean bowl. Add the vegetables and mix to combine. Allow to marinate overnight. Giardiniera will only get better with time. After 2 days at the most in the bowl, you can place the Giardiniera in air-tight mason jars and keep in the fridge for 2 to 3 weeks.