Preheat your oven or toaster oven to 350 F.
Add one teaspoon of olive oil to a pan or griddle over medium-high heat.
Add sliced onion and sauté for 3 to 4 minutes until the onion starts to soften and turn a little bit darker.
Add the bell pepper and mushrooms and cook them with the onion for an additional 3 minutes. Then remove the veggies to a bowl while you cook the steak.
Add another teaspoon of oil to the pan or griddle and then add the steak. Season the steak with seasoning salt and do not touch the steak for 3 minutes to allow it to brown just a bit.
After 3 minutes, stir the steak and add salami. Sprinkle on a bit more seasoned salt and cook the steak and salami for an additional 2 minutes.
While the steak and salami are cooking, slice the bread roll, and open it like a book. Add it to the preheated oven to toast lightly for about 3 minutes.
Add the cooked veggies back into the pan or griddle with the steak. Stir everything together and then arrange the meat and veggies in a shape that's about the size of your bread roll. Top everything with cheese and turn off the heat under the pan, allowing everything to stay warm in the pan.
Spread some mayonnaise onto the inside of the bread roll and then, with one or two spatulas, move the cheese-covered meat and veggies into the roll.
Serve and enjoy.