In a small saucepan, mix soy sauce, peanut butter, honey, rice vinegar, sesame oil, minced garlic, minced ginger, Chinese five-spice powder, and sriracha (if using). Whisk until smooth.
In a separate bowl, stir together cornstarch and water until the cornstarch dissolves.
Add the cornstarch mixture to the saucepan. Continue to cook, stirring, until the sauce thickens, about 2 to 3 minutes.