Add the diced onion, minced garlic, and grated ginger to the slow cooker.
Stir in the drained chickpeas, diced tomatoes, coconut milk, garam masala, turmeric, paprika, salt, and black pepper.
Cover and cook on low for 6 hours or on high for 3 hours until the sauce thickens and the flavors meld.
About 45 minutes before the curry is done, combine the brown rice and water in a medium saucepan. Bring to a boil, then reduce to a simmer, cover, and cook for 40 minutes until the rice is tender.
Fluff the rice with a fork. Serve the chickpea tikka masala over the brown rice and top with chopped cilantro.