Place the beef cubes, chopped onion, and minced garlic into the slow cooker.
Sprinkle the curry powder, turmeric, salt, and black pepper over the beef and vegetables. Stir to coat evenly.
Add the cauliflower florets, beef broth, and coconut milk. Stir once more to combine.
Cover and cook on low for 7 to 8 hours until the beef is fork-tender.
Stir in the fresh spinach during the last 10 minutes of cooking so it wilts without becoming mushy.
Taste and adjust salt if needed before serving.