Preheat oven to 375°F.
Heat the oil in a medium sauce pan over medium-high heat. Add diced peppers and onions and cook until soft (about 3-5 mins).
Add the steak and cook until browned. Remove from heat and set aside.
Using a rolling pin, flatten each slice of bread.
Tip: choose slices from the center of the loaf so they are larger in size.
Add a small amount of the cheesesteak mixture to the bottom right corner of each bread slice (so that about half the bread is covered, in a triangle shape). Be careful not to overstuff, and leave some room along the outer edge of the bread.
Top each sandwich with shredded cheese.
Take the top left corner of the bread (where there is no filling) and fold it along the diagonal to meet with the bottom right corner, forming a triangle shape. Line up all the edges to make a triangle, then crimp with a fork to seal.
Brush the tops of the sandwiches with egg wash then transfer to a prepared baking sheet.
Bake for 5-10 minutes or until golden brown.
Recipe adapted from: www.cookingdivine.com