Place the potatoes into a pan hot boiling water and cook for 15-20 minutes or until they are soft.
Drain the potatoes and leave in the hot pan (off the heat of the hob) so that any leftover moisture evaporates.
In the meantime, heat the vegetable oil in a pan and add the onions and carrots with the pinch of salt.
Cook the onion and carrot for 8 - 10 minutes or until they have softened.
Add the mushrooms, lentils and garlic to the pan and cook for another 8 - 10 minutes or until the mushrooms have softened and any additional moisture has begun to cook off.
Add the tomato puree, miso paste, cornflour and mixed herbs then stir until well combined. You want to avoid the cornflour forming any lumps.
Pour in the vegetable stock and simmer for 10 minutes or until the sauce has thickened.
In the meantime, mash the potatoes along with the non-dairy milk and butter. Season with a little salt and pepper.
Stir the frozen peas into the miso mushroom mix before transferring to an oven dish.
Top with the mashed potatoes (using a piping bag with a star nozzle to create a pretty pattern) until the whole pie is covered.
Place into the oven at 180C / 356F / gas mark 4 for 10-15 minutes until the gravy is bubbling and the top is browned and crispy.