Prepare the couscous in boiling salted water according to the instructions on the packet. Clean the peppers, remove seeds, wash, dice and add to the couscous. Season with salt and pepper. Wash parsley and mint and pluck leaves from the stalks.
Finely chop the parsley and add to the couscous. Clean the mushrooms and remove the stems. Fill mushrooms with couscous. Cut mint into fine strips and mix with yoghurt. Season with salt, pepper and 1 pinch of sugar.
Spread the grill tray with oil if necessary and place the mushrooms in it. Grill on the preheated grill for 10-15 minutes. Serve mint yoghurt with the mushrooms.