Preheat oven to 350℉. Mince the garlic, dice the onion, chop the mushrooms, and shred the cheddar cheese (or use pre-shredded cheese). Set aside.
Over medium heat, add a tablespoon of extra-virgin olive oil or butter to a skillet and cook the ground beef and onions until the meat is fully cooked (about 5-7 minutes). Once the beef mixture is cooked and there is no more pink in the meat, drain the excess oil and transfer the ground beef to the casserole dish.
Layer the vegetables (green beans, peas, and carrots) on top of the ground beef in the dish.
Use the same pan that you cooked the ground beef in to make the homemade cream of mushroom soup. First, melt the cubed butter over medium heat. Then add the minced garlic and flour. Whisk the ingredients until a thick paste forms. Then add the chopped mushrooms, chicken broth, and slowly whisk in the heavy cream. Add the salt, pepper, garlic powder, and minced onion.
Allow the soup to cook and thicken for about 5 minutes. Then pour the soup over the vegetables in the baking dish.
Sprinkle 1 1/2 cups (save 1/2 cup of cheese for later) of the shredded cheese over the soup. Finally, line a single layer of tater tots over the shredded cheese. Cover dish with aluminum foil and bake for 30 minutes. After 30 minutes, take the dish out of the oven, sprinkle the hotdish with the remaining 1/2 cup of shredded cheese and bake for another 30 minutes uncovered.
The hotdish will be done when the hotdish is bubbling, the cheese is melted, and the tater tots are golden brown. Let it rest for a few minutes before serving. Enjoy!