Heat 1 tbsp of oil in a pan and add the ground beef, brown until no longer pink inside, season with salt and pepper and remove to a separate plate.
To the same deep pan add the butter and melt it, bring in the finely chopped mushrooms and cook them over medium heat until golden and the liquid has evaporated. Then add the chopped onion and cook over low heat for 5 minutes, add minced garlic and cook for 30 seconds longer.
Now sprinkle the flour all over the mushrooms and stir to combine, then add in the chicken stock and scrape down the bottom of the pan to release the brown bits into the sauce, bring to a boil, then lower the heat and add the cream, Worcestershire sauce, soy sauce and pepper.
Start preheating the oven to 180C/350F. Bring the beef back into the pan together with the frozen veg mix, and turn the heat to a medium, allow the mixture to come to a boil, then lower the heat and add more salt if needed.
Transfer the meat mix to a baking pan or a casserole dish, top with the tater tot and bake in the preheated oven for 40-45 minutes until the tots are golden and crispy.