1) In a large skillet or flat griddle over medium-high heat, saute the onions and peppers in butter for several minutes until softened.
2) Place sausages on the griddle or in the skillet next to the peppers and onions. Flatten slightly to the length of your hoagie roll.
3) Cook sausages for approximately 4 minutes per side or until internal temperature reaches 68C on an instant-read thermometer.
4) Place half of the peppers and onions on top of two sausage links placed side by side and top with three slices of provolone cheese. Repeat for second sandwich. Wait for cheese to slightly melt. Pick up sausage and peppers from underneath with a metal spatula and place in hoagie roll.
Season with salt and pepper and serve with a side of warm marinara sauce. Enjoy!