Make the sauce: In a bowl, whisk peanut butter, coconut milk, soy sauce, brown sugar or honey, lime juice, rice vinegar, garlic, ginger, sriracha, and fish sauce (if using) until smooth.
Load the slow cooker: Place chicken thighs or breasts in the crockpot. Pour the sauce over the top and turn the chicken to coat.
Cook low and slow: Cover and cook on Low for 4–5 hours or High for 2–3 hours, until chicken is tender and easily shredded.
Add veggies (optional): If using quick-cooking veggies like bell peppers or snap peas, stir them in for the last 30–45 minutes so they stay crisp-tender.
For sturdier veggies like carrots or broccoli, add them in the last 60–90 minutes or steam separately and stir in at the end.
Thicken the sauce (optional): If you prefer a thicker sauce, whisk cornstarch with 2 tablespoons water, stir into the crockpot, and cook 10–15 more minutes.
Shred or slice: Remove chicken, shred or slice, then return it to the sauce. Taste and adjust with more lime, soy, or sriracha.
Serve: Spoon over hot jasmine rice or toss with rice noodles. Top with cilantro, green onions, crushed peanuts, and a squeeze of lime.