I learned this trick in a restaurant! The chicken breast melts in your mouth

Ingredients:
butter: 200 g (7.1 oz)
chicken breast: 1 pc
salt: 5 g (0.2 oz)
black pepper: 2 g (0.1 oz)
eggs: 2 pc
milk: 100 ml (3.4 fl oz)
flour: 50 g (1.8 oz)
mozzarella: 200 g (7.1 oz)
salt: 3 g (0.1 oz)
black pepper: 1 g (0 oz)
oregano: 2 g (0.1 oz)
tomatoes: 3 pc
mozzarella: 150 g (5.3 oz)
onion: 3 pc