Beef and Cheese Gyoza

1. For the spicy dumpling sauce, mix the ingredients and set aside. 
2. To make the gyoza filling, place the ground beef, scallions, egg, ginger (Note: Ginger is mentioned here but not in ingredients list, assuming it's an oversight or optional), garlic, and salt in a large bowl. Mix vigorously for 3-4 minutes or until the mixture is well combined and sticky. 
3. Place a tablespoon of filling into the center of the gyoza wrapper and top with a strip of mozzarella. Moisten the edges of the wrapper with a little water and then bring the sides up over the filling and seal at the top only (leave the sides open). 
4. Heat the avocado or vegetable oil in a large non-stick frying pan over high heat. Add the gyoza and cook for about 2 minutes or until the bottoms are starting to turn golden brown. Pour in enough water to come a quarter of the way up the sides of the gyoza. Cover with a lid and steam for 5 minutes. Then remove the lid and allow the water to evaporate so that any cheese that has leaked out the sides gets super crispy and brown. Transfer to a plate and serve warm with the dipping sauce.