Heat the oil in a skillet over medium heat. Add the onions with a pinch of salt to sweat them. Cook for 5 minutes. Add the peppers. After about 5 more minutes, add the garlic. Cook an additional 2 minutes. Remove the pan from the heat and let the vegetables cool.
In a large bowl add in all additional ingredients except for the prosciutto, marinara and fontina cheese. Once the peppers and onion mixture has cooled, add to the meat mixture. Combine all ingredients together. Form into a loaf. Make a trench down the middle and add the fontina cheese. Surround the cheese with the meat so its completely covered.
Wrap the prosciutto around the meatloaf so its covered. Cover with 2 cups of the marinara.
Cook in the oven for 60 minutes. Remove and slice. Serve with additional marinara.