Add the vegetable broth, dried lentils, drained chickpeas, diced tomatoes, frozen carrots, and frozen bell peppers to the slow cooker.
Stir in the cumin, coriander, cinnamon, turmeric, salt, and black pepper until the spices are evenly distributed.
Cover and cook on low for 6 to 7 hours or on high for 3 to 4 hours until the lentils are soft and the stew has thickened.
Stir once halfway through if possible, then serve once the cooking time is complete.