Green pepper, seeded and cut into lengthwise strips. Onion, cut into lengthwise strips. Pierce casing of sausages with fork. Cook in a large skillet over medium-high heat along with bell pepper and onions, until sausage is brown on all sides. Remove pepper and onions; keep warm.
Blend spaghetti sauce into pan. Bring to boil; cover and reduce heat to low. Simmer for 10 minutes or until sausage is no longer pink.
Slice each bun lengthwise; fill each with a piece of sausage and sauce. Top with peppers and onions. Sprinkle each sub with an equal amount of cheese. Serve.