Add butternut squash, coconut milk, chicken broth, onion powder, brown sugar, sriracha sauce, lime juice, garlic powder, and curry powder to slow cooker. Cover and cook on high 2-3 hours or on low 4-5 hours.
Blend mixture until smooth using an immersion blender, regular blender, or food processor. (You may need to do this in batches depending on your available equipment) Return mixture to slow cooker. Add salt to taste and milk to think to desired consistency.
Just before serving, prepare the gremolata. In a small bowl stir together cilantro, peanuts, lime zest, and red chili pepper flakes. Serve soup warm and top with gremolata.