Add the sliced onion, minced garlic, and grated ginger to the bottom of the slow cooker.
Pour in the coconut milk along with the lime zest and juice. Stir in the salt and pepper until combined.
Layer the chopped bok choy and snow peas over the sauce mixture.
Cover and cook on low for 3 hours until the vegetables are mostly tender.
Place the tilapia fillets on top of the vegetables, cover again, and cook for 30 to 45 minutes more until the fish flakes easily with a fork.
Serve the fillets and vegetables in bowls with the sauce spooned over the top. Sprinkle with chopped cilantro before eating.