Heat the oil (or vegan butter) in a large pan over medium heat. Add the onions and mushrooms and sauté for about 5 minutes until browned, stirring occasionally. Add garlic and roast for a further minute.
In a jar, mix the flour (or cornstarch), soy sauce and mustard with a bit of the vegetable broth until smooth, so there are no lumps from the flour anymore.
Then add the flour mixture to the pan along with the remaining vegetable broth.
Stir constantly and bring to the boil. Reduce the heat and let simmer until it thickens up to your desired consistency, about 5 minutes. (The longer you cook, the more it thickens). Season with thyme, salt, and pepper to taste. Refine with coconut milk if you like.
Add the no-meat balls to the gravy and stir to coat.
Serve vegan meatballs and gravy over mashed potatoes. Enjoy!