Cook time: 25 mins
- Preheat the barbecue to medium-high heat. Add the rye bread and fry until lightly toasted.
- Add 2 tablespoons of butter to the barbecue plate and add onion and mushrooms. Fry until well cooked, then season with salt. Set aside.
- Add the patties to the grill. Cook for 13-15 minutes, turning every 3-4 minutes, until fully cooked.
- To assemble, top patties with mushroom onion mix and lay 2 mozzarella slices on top of each. Pop a lid on the pan and cook for 30 seconds, until the cheese is melted.
- Slather garlic mayo on top of rye slices and top with cheesy melt. Serve whilst hot and deliciously melted.