Step 1: – slice your onion in half, and then slice one half again to get a quarter. Cut slices across the "rings" to get nice strips.
Step 2: – heat butter in a non-stick pan on medium-low
Step 3: – once it’s hot, throw the onions in the pan.
Step 4: – slice the mushrooms and add them once the onions are a bit soft
Step 5: – chop or slice the roast beef into bite-sized pieces or smaller. Add them to the pan. Season with salt and pepper
Step 6: – continue cover + simmer, stir, cover + simmer, stir until the mushrooms are soft as well as the onions, and the beef warmed.
Step 8: – make a grilled cheese with the bread, butter and cheese
Step 10: – once it’s made, separate the grilled cheese.
Step 11: – mix about half a tablespoon (maybe a little more) of the dressing in with the onions, mushrooms and beef.
Step 12: – scoop all the mixture onto one half of the grilled cheese, close it, and enjoy!