Place the rinsed lentils, diced onion, minced garlic, and grated ginger into the slow cooker.
Add the curry powder, cumin, salt, and black pepper, then stir to coat the lentils and vegetables.
Pour in the vegetable broth and coconut milk. Stir everything together until the spices are evenly distributed.
Cover and cook on low for 7 hours until the lentils are soft and the stew has thickened.
Stir in the fresh spinach leaves during the final 10 minutes of cooking so they wilt but stay green.
Taste and adjust salt if needed, then serve hot.