Preheat oven to 425F [218C].
In a pot add the cauliflower and boil for 20 minutes until cauliflower is fork tender.
In a pan add the oil along with the carrots, corn, peas and onions on a medium heat. Season with a pinch of salt and pepper. Sauté for 3-5 minutes.
Then add in the vegan ground beef crumbles.
In a small bowl combine the cornstarch and 2 teaspoons of vegetable broth to make a slurry. This helps to thicken the gravy and filling. Add it into the pan and mix with a spatula. Then add in the remaining vegetable broth.
Cook this for about 5 minutes over medium heat. It should thicken slightly but still be a bit liquidy because it will thicken more in the oven. Season with the garlic powder, onion power, thyme, rosemary, black pepper and salt if you like.
Once the cauliflower is done drain it. Add the vegan butter, non-dairy milk and salt to taste. Mash with a fork until smooth.
In an oven safe dish add the filling then top with the mashed cauliflower.
Bake for 25-30 minutes and broil for 5-7 minutes. It should be firm to the touch and a bit golden on top.
Allow to cool for 10 minutes before cutting into it. Garnish with extra thyme and black pepper.