Roast Beef Cheese Omelet

I grilled chopped onions with two slices of chopped roast beef. I used two eggs, 1/2 tsp of mirin, 1/2 tsp soy sauce, a pinch of pepper. After making the sheet of egg, I placed one slice of american cheese, the roast beef and grilled onions inside and folded it into a rectangle shape. I took a plate and flipped the omelet over to retain its shape. I topped it off with ketchup and Kewpie Japanese mayo.