Heat a large non stick pan with 1 tablespoon of oil on high heat. When hot, ad the sliced spring onion white parts, aromatic paste, and the diced mushrooms, stir often and cook until the spring onion is softened. Add the pork, soy sauce, oyster sauce, fish sauce, sugar, and water chestnuts (if using). Break the ground pork up as it cooks with your spatula, until cooked through and no liquid remains in the pan. Set the pan aside, this is the dumpling filling, and allow this to cool to room temperature.