Place peanut butter in a medium bowl.
Add soy sauce, lime juice, rice vinegar, and brown sugar.
Stir in minced garlic and grated ginger if using.
Add chili paste a little at a time, tasting for desired heat.
Whisk in sesame oil and fish sauce if using for extra depth.
Gradually add warm water or coconut milk to reach the desired consistency, whisking until smooth.
Taste and adjust seasoning: more lime for brightness, sugar for sweetness, or soy for saltiness.
For a thinner dressing add additional warm water 1 tablespoon at a time.
Transfer to a serving bowl and garnish with chopped toasted peanuts and a lime wedge.
If using as a glaze for satay, warm gently over low heat before brushing on skewers.