Prepare the flax egg by mixing 1/2 table spoon of ground flaxseeds and 1 1/2 table spoons of hot water together. Set aside.
Heat the oil in a wok or a frying pan and cook the mushrooms, carrot and red pepper. Some moisture will come out from the mushrooms. Cook until most of the moisture go.
Add in the onion and garlic and continue frying until cooked. Add in the garden peas, cook for a minute then stir in the wine (if using), soy sauce, tomato puree, Dijon mustard and dry mixed herbs. Leave to simmer for a couple of minutes. Stir in between if necessary.
While the vegetable mixture is simmering, *put the lentils in a beaker and using an immersion blender, pulse for a few seconds. Do not blend too much, we want some textures remain in the wellington filling.
Add the lentils. salt, black pepper and the prepared flax egg into the simmering vegetable and give it a good mix. Continue cooking for one minutes. If your mixture looks a little bit too moist, add some bread crumbs to adjust **the consistency.
Turn off the cooker and Stir in the vegan cheese. Transfer the mixture to a ceramic bowl and leave to cool down.
Preheat the oven to 200°C (gas mark 6) and prepare a baking tray lined with baking paper.
spread some flour on a work table and roll the block of puff pastry to a thin pastry sheet.
Put the vegetable and lentil mixture in the centre of the pastry sheet and form a log shape with a spoon.
Fold both of the long sides. If the sides are not sticking together well, put some water on one of the sides with your finger and stick it back again. Press gently with a folk if necessary.
Fold the two ends. If you have too much excess on these ends, cut some off before folding. Use water to stick again if necessary.
Flip over the wellington so that you won't see the folded lines. form a nice wellington shape with your hand!
Make some cuts in places on the top.
Bake for 40 to 45 minutes. Baking temperature and time vary depending on the type of the puff pastry you are using. Follow the cooking instructions on the package.