Preheat the oven to 350°F (180°C) and brush the oil on the bottom of a a 9 x13 casserole dish.
In a frying pan on medium heat, brown the ground beef, remove the pan from the heat, while preparing the vegetables
Peel and thinly slice the potatoes with a mandolin or a sharp knife.
In a medium bowl pour in both the mushroom soup, add the milk and whisk to mix them together well.
To the casserole dish add a layer of potatoes, broccoli, cauliflower, spinach, then beef and cheese.
Pour the soup on top of the potatoes, broccoli, cauliflower, beef and cheese, then add one more layer of potatoes and then a generous layer of cheese.
Cover the dish with tin foil and bake it for 1 hour and 15 minutes.
Remove the foil and bake for another 30 minutes or until the potatoes are soft and cooked through and slightly crispy on top
Allow the dish to sit for 5 to 10 minutes before serving.