Peel potatoes; leave whole and toss them in a crockpot on low for 6-8 hours.
Preheat oven to 400ºF. Spray a baking sheet with cooking spray.
Heat oil in a skillet over medium. Finely chop onion and garlic, or add to a food processor and pulse. Add to hot oil and cook for 3-4 minutes.
Add mushrooms to food processor and pulse until finely chopped. Toss into skillet with onion. Cook for 5-7 minutes more, stirring occasionally. Remove from heat and pour into a bowl, allowing to cool.
Add the raw beef, egg, Worcestershire sauce, salt, and pepper to the mushrooms and onions; mix well. Scoop into muffin cups and sprinkle cheese on top.
Bake for 20-25 minutes until internal temperature reads 160°F and beef is no longer pink in the center.
Steam peas. Stir in 1 teaspoon of lemon zest and 1 tablespoon of butter.
Mash potatoes with 2-3 tablespoons of butter and 1/4 cup of milk. (Add more liquid if potatoes are too thick).
Serve meatloaves with peas and potatoes on the side.