Hash brown omelette stuffed with mushrooms, red pepper and spinach

MAKES FOUR

30ml butter1 large potato with skin on, grated2 large eggs30ml fat-free milk15ml olive oil1 onion, finely chopped1 garlic clove, finely chopped150g small button mushrooms, halved½ red bell pepper, cubed50g spinachSalt and freshly groundblack pepper, to taste45ml mozzarella, grated60ml sour cream, to serve