This works well if things are done ahead to help move things along. Cut onions/peppers and lightly saute/wilt and have handy. Brown bacon cut into half strips, brown and crumble breakfast sausage, chop some ham into 1/2″ cubes. Have shredded cheddar handy. If mushrooms are desired, use canned ones and drain well before hand. Use two 12″ skillets for this.
Toss a lump of butter in one pan and melt over medium heat. Add hashbrowns until you have an even layer maybe 2″ thick. Cover and cook until browned on the first side. Set the other pan atop of the first and quickly flip so the hashbrowns are now in the fresh pan cooked side up. Use a spatula’s edge to score the hashbrowns into two halve…they can be loosely connected. On one half add your fillers starting with cheese and ending with cheese and then flip the other side over the filled side. I add another chunk of butter at this point and cover and cook until the side in the pan is brown, then flip and do the other side. Transfer to a cookie sheet in a warm oven kept at 250 degrees and loosely cover with foil. Do this with each subsequent pan full until you have enough to serve a meal.
There’s no right or wrong with fillers and you can make these as large as you want. Done as described though you better sit down hungry. This sounds like a lengthy process but if the veggies and meats are done ahead it doesn’t take all that long and eggs can be served on the side.