Whisk together coconut milk, chicken broth, peanut butter, soy sauce, brown sugar, ginger, garlic, and salt in a 3 ½- to 4-quart slow cooker until smooth.
Add chicken to slow cooker; stir to combine.
Cover and cook on Low for 5 to 6 hours or on High for 2 ½ to 3 hours, until an instant-read thermometer inserted into the thickest part of the chicken reads at least 165 degrees F (74 degrees C).
Stir together cornstarch and water in a small bowl. Add to the slow cooker, stirring until combined. Cover and cook on High for 15 minutes, or until thickened.
Stir in lime juice, Sriracha, and fish sauce, if using.
Garnish with peanuts, cilantro, and additional Sriracha. Serve with lime wedges.
