In a large skillet, melt butter over medium-high heat. Once butter is sizzling, sauté mushrooms until golden brown, about 5 minutes. Then transfer to a plate and set aside.

Add onions into same skillet and sauté until slightly caramelized, about 5-6 minutes.

Add peppers into skillet with onions and cook until peppers get soft, about 3-4 minutes. Then set onions/peppers aside with mushrooms.

Add pot roast into pan and cook until all meat is browned, about 5-6 minutes. Season pot roast with spices and add all veggies back into skillet. Stir to fully combine.

Using a spatula, section off each serving in your pan and place cheese slices directly over each serving. Take off heat and allow residual heat to melt cheese onto steak mixture.

Lightly toast buns and smear with a bit of mayo, if desired. Serve!