Heat a large pan over medium heat. Add the olive oil to the pan, when oil is hot, add the onions and turn the heat down to low. Allow the onions to caramelize for about 20 minutes. To do this, keep the heat low, stir only occasionally and add about 2 TBSP water to the pan every 3-5 minutes- or when the pan is very dry and you are worried the onions may burn- to help the onions caramelize without burning. Stir after you have added the water but leave the onions to caramelize while the water evaporates.
While you are waiting, prep the rest of the mixture: finely chop the garlic and the parsley and combine in a bowl with the ground beef, cheddar cheese, garlic powder, mustard and salt and pepper.
When the onions are brown and caramelized, push them to the outskirts of the pan. Toss the mushrooms into the pan and allow them to cook, undisturbed for 2 minute. Stir and then let cook another minute.
De-glaze the pan by adding 1 TBSP water. Turn off the heat and stir, be sure to scrape the bottom of the pan. Water should evaporate within a minute.
Allow the onion mixture to cool a bit, then stir it in with the ground beef and cheese mixture.
Preheat the oven to 450F.
Scoop ~2 tsp of the mixture into a wonton wrapper. Wet the edges with water and seal them together. Place them on a sheet pan/cookie sheet or baking tray that has been LIBERALLY sprayed with pan spray. Repeat with the remaining filling until you are out of filling.
Before putting them in the oven, spray the wontons with pan spray, again, be generous. Bake for 6 minutes or until golden and crunchy on the outside and ground beef is cooked through.
Notes
This makes ~25-30 wontons but can easily be doubled. It also freezes well, so go ahead and make the wontons ahead of time, but do not cook. Freeze on a sheet pan for at least 20 minutes, then transfer to a ziploc or tupperware container. When ready to eat, remove from the freezer right to the oven. Increase cooking time 3 minutes.
Recipe by Super Foods Life at https://www.superfoodslife.com/cheeseburger-wontons/