Put onion, carrots, coconut milk, curry powder and 1/4 cup water in slow cooker. Season lamb with salt and pepper on all sides.
Heat a large skillet over medium-high heat until hot. Add 1 Tbsp. oil. Add one-third of lamb and cook until browned all over, about 6 minutes. Transfer lamb to slow cooker. Repeat with remaining batches of lamb and 1 Tbsp. oil.
Add 1/2 cup water to skillet, scraping pan with a wooden spoon to incorporate browned bits. Pour liquid into slow cooker. Cover and cook on high for 4 hours.
In final half hour of cooking, skim fat off stew and discard. Stir in chickpeas and continue to cook. Serve lamb over basmati or other white rice.
