Place the pizza and tomato sauces into a large pot over medium heat.
In a large Dutch oven, heat a splash or two of oil over medium-high heat. Working in batches, add the sausages, browning on all sides. Transfer browned sausages to the pot of sauce.
Add more oil to the Dutch oven and add all of the vegetables. Saute until just starting to get soft, then transfer to the pot of sauce along with the sausages.
Season with salt and pepper, Italian seasoning and red pepper flake.
Cover, reduce heat to medium-low and simmer for 5-6 hours, stirring occasionally.
Slice the bread in half. I prefer to do this by cutting a 'V' down the top of the bread, making a trench for the sausages and sauce. I find that the bread doesn't split so easily this way. I also remove some of the bread inside just to make more room for the great toppings.
Cut bread into lengths a tad shorter than the sausages.
Add meat and top with sauce and a little bit of the vegetables.
Top with cheese and place on a sheet pan under the oven broiler just long enough to melt the cheese.