Begin by heating the olive oil in a skillet over medium heat. Once warm, add in the sliced onions and bell peppers. Sauté until they are soft and slightly caramelized. This should take about 7-8 minutes.
To this mix, add the minced garlic, salt, and black pepper. Stir occasionally and cook for another 2 minutes. Once done, set this mix aside.
In the same skillet, place your thinly sliced steak. Depending on the thickness, it should take about 3-4 minutes on each side to cook to a medium-rare finish. Once cooked to your liking, set the steak aside.
Lay out your slices of bread. On one side, layer two slices of Pepper Jack cheese, followed by half the steak slices, and then half of your onion-pepper mix.
Place another two slices of Pepper Jack cheese on top to ensure the Pepper Jack Steak Grilled Cheese has ample melty goodness.
Top with the second slice of bread. On the outer parts of both bread slices, spread a generous helping of butter.
In a clean skillet or griddle over medium heat, place your assembled Pepper Jack Steak Grilled Cheese. Grill each side until they are golden brown and the cheese has melted. This should take about 3-4 minutes on each side.
Once cooked to perfection, remove from the skillet, let it sit for a minute, then slice in half and serve!