Place the rinsed lentils, diced onion, sliced carrots, minced garlic, and diced tomatoes into the slow cooker.
Add the vegetable broth, curry powder, salt, and black pepper.
Stir everything together until the spices are evenly distributed.
Cover and cook on low for 7 hours or on high for 3 to 4 hours, until the lentils are soft and the soup has thickened.
Ladle into bowls and top each serving with a few cilantro leaves.