Into a pan on low heat, add butter and let it melt.
Cook the garlic for 2 mins. (It should not turn brown but should infuse the butter slowly).
Add mushrooms and coat with butter and leave undisturbed for a few minutes so that it can brown. Stir and cook few minutes more, adding a pinch of pepper at the same time, followed by soy sauce.
Mix in the chopped up spinach and cook until wilted. Switch off the flame and add a pinch of chilli flakes.
Transfer the mushroom mixture into another bowl and mix in mozzarella cheese.
Now to assemble the sandwich: Spread butter and toast 4 slices of wholemeal bread on both sides. Divide the filling and fill both the sandwiches then toast it to melt the cheese.
This quick and easy finger licking mushroom melt sandwich is ready to serve. Enjoy!!