1. Add butter to a grill pan and set to medium heat.
2. Place portobello mushroom on to grill pan and season with salt and pepper.
3. Gently press down on the mushroom with a grill press and cook for 1 min on each side or until cooked through, set aside.
4. Toast all 4 slices of bread till golden on both sides.
5. Spread 1 Tbsp of Tomato sauce on two slices of the bread, add emmental cheese, shredded cabbage, portobello mushroom, spinach, diced tomato and top with remaining slice of bread.