In a large skillet, cover just the bottom with water & add sausages, cook over medium heatuntil done, turning frequently. The water will evaporate, so you get the nice brown marks on each side.
While sausages cook, in another skillet, over medium heat, add 1-2 tablespoons of oil, then sliced peppers & onions. Add Seasonings to taste. Cook until crisp tender stirring often.( they usually are done about the same time as the sausages.
Put sub rolls on lined pan & put a layer of cheese in the bottom. Add sausage(I usually cut the sausage in half & stagger them in the bun because the rolls I buy are longer than the sausages)
Add peppers & onions, top with cheese.
Put in the oven & bake until cheese is melted & bun is slightly crusty. Enjoy!