Peel the onion and chop along with the mushrooms, and pepper into thin strips. Cut the baguette into 2 pieces
Put a large non-stick pan on a high heat and add 1 tbsp of oil, when hot add the mushrooms and cook for 3-4 minutes without stirring. we are looking to get a lovely meaty char to the mushrooms
Put another pan on medium heat and add 1 tsp of oil, once hot add the onion and peppers and fry for about 5-8 mins stirring occasionally until they go nice and brown. Remove and set aside
Add another large empty pot to cover and weigh down the mushroom, this will help the charring even further, cook for 2-3 minutes, give the mushrooms a stir, then press again for another 2-3 minutes,remove the pot and add the tamari and stir it around so each mushroom gets infused with the flavour and and remove the mushrooms from the pan and set aside.
Remove half the mushrooms from the pan and add the slices of cheese and cook on a medium heat until it starts to melt and coat each of the mushrooms.
Spread and ½ tbsp of mustard and 1 tbsp mayo on each baguette, add a few leaves of rocket or mixed leaves. Add the cheesy mushrooms, add the on the onions and peppers and finish with some of the charred mushrooms