Place the finely diced onion, minced garlic, grated ginger, chopped lemongrass, Thai red curry paste, fish sauce, full-fat coconut milk, and honey into the bowl of the crockpot; stir to combine.
Add the diced chicken and the chopped broccoli rabe to the crockpot and toss gently so the ingredients are evenly distributed in the curry base.
Cover and cook on LOW for 5–6 hours or on HIGH for 4–5 hours, until the chicken is cooked through and tender.
Just before serving, stir in the chopped basil and/or cilantro.
Serve the curry over steamed rice and top with pomegranate arils, chopped peanuts, and extra herbs if desired.