Food Hacks: Sous Vide Burger with Portobello 'Buns'

Ingredients

• 2 pounds (0.45 kg) ground beef
• 1 large egg
• Salt and freshly ground black pepper
• 12 burger-sized Portobello mushrooms
• 1 cup (237 ml) water
• 1/4 cup (59 ml) extra virgin olive oil
• 12 slices mozzarella
• 1 large tomato, sliced
• 6 leaves butter lettuce (or lettuce of your choice)