Combine soy sauce, water, fish sauce, sesame oil, rice vinegar, chili sauce, and brown sugar substitute in a small saucepan. Begin heating the ingredients on the stove until they just start to simmer. Don’t overheat the saucepan.
Whisk peanut butter into the sauce. Once the peanut butter is broken up, the sauce will thicken slightly. Then, take it off the heat right away. It will still be in a fairly liquid state.
Now grab whatever you are cooking with your pad thai sauce. In this case, it’s shirataki noodles, which are not included in the ingredients. Cook your ingredients in a pan or pot, then add the pad thai sauce to the ingredients while the heat is still hot. The sauce will reduce quickly and thicken around your ingredients.