Wash the rice in cold water, cook it and let it cool down. Then add the rice winegar.
Heat up oil in a pan and add the mushrooms, corn and peeled prawns. Stir fry everything, but don’t overcook the prawns as they may become stiff.
Take it out of the heat and prepare the sauce by mixing ketchup, oyster sauce and sugar together.
Now prepare your assembling station. I recommend starting with a plastic wrap, cutting a piece that is a little bigger than your nori sheet. Then put the nori sheet on top of it.
Make the sandwich by following the steps: Form a 10 cm circle of rice in the middle of the nori, then add the prawns, sauce, corn and mushrooms, cover it with 1 lettuce leaf and place another layer of rice on top. Bend the corners of the nori to the middle of the rice and wrap everything in plastic wrap.
You should have 2 sandwiches wrapped in a nori and plastic wrap. Let them cool down in a fridge so they can be easily cut.
Cut them in half with your knife, then remove the plastic wrap and enjoy!