Heat a large frying pan over medium-high heat and melt the butter.
Add the mushrooms to the pan and cook until golden brown.
Stir in the garlic, chili, and oregano, cooking for another minute.
Season the mixture with salt, pepper, and a splash of lemon juice. Remove from heat and set aside.
Mix the mozzarella and cheddar cheese, then divide the cheese between four slices of bread.
Top the cheese with the cooked mushrooms and sandwich with the remaining slices of bread. Butter both sides generously.
Preheat a non-stick pan over medium heat, then cook the sandwiches until golden brown and crispy on both sides, and the cheese has melted. Slice and serve.