Add the rinsed lentils, coconut milk, Thai red curry paste, diced onion, minced garlic, grated ginger, sliced carrots, diced bell pepper, vegetable broth, and salt to the slow cooker.
Stir everything together until the curry paste is mostly dissolved into the liquid.
Cover and cook on low for 6 hours or on high for 3 hours, until the lentils are tender and the carrots are soft.
Stir in the fresh spinach during the last 10 minutes of cooking so it wilts but stays bright.
Spoon the curry over cooked brown rice in bowls and finish with a squeeze of lime and a sprinkle of cilantro.