Simmer italian sausage in water till done. Then brown outside of sausage in skillet. Meanwhile cook veggies in a couple TBL of olive oil till tender, season with salt & pepper to taste if desired.
Place two slices of provolone on each sub bun. Cut each sausage link in half longwise and place both slices on bun, then top with veggies, and add grated mozzrella cheese. Pop in broiler for a couple of min. to melt cheese.