Cut off hard parts from the stalks and roots of the mushrooms.
Halve or quarter large mushrooms. Leave small mushrooms whole.
Mix all the ingredients for the marinade in a bowl. Add some water to thin it out a bit. Toss the mushrooms in the marinade and mix until all of the mushrooms are coated in the marinade.
Place the mushrooms on a baking sheet lined with parchment paper and bake in the preheated oven for 25 minutes.
Prepare vegan omelet:
While the mushrooms are roasting in the oven, let's prepare the omelet.
Blend all ingredients except the vegetable oil in a blender until smooth. The batter should be about the consistency of pancake batter.
Heat some vegetable oil (not much) in a non-stick pan over medium-high heat. Pour the vegan egg mixture into the pan in portions and spread it out by shaking the pan.
Fry the omelette for about 3 to 4 minutes . Turn and finish frying.
Slide out of the pan.
Arranging and serving:
Take mushrooms out of the oven.
You could serve the mushrooms on top of or in the omelette, or like I prefer, shape the omelet into a roll or bag and serve the mushrooms with it.