In a 4-quart or larger electric slow cooker, lightly mix thinly sliced onion, garlic, ginger, cinamon stick, cumin, red pepper flakes, turmeric, cloves, and cardamom. Rinse chicken and pat dry; then arrange, overlapping pieces slightly, on top of onion mixture. Pour in broth. Cover and cook at low setting until meat near thighbone is very tender when pierced (6 1/2-7 hours).
Carefully lift chicken to a warm serving dish and keep warm. Skim and discard fat from cooking liquid, if necessary; remove and discard cinnamon stick. Blend in cornstarch mixture. Increase cooker heat setting to high; cover and cook, stirring 2 or 3 times, until sauce is thickened. Season to taste with salt; stir in cilantro and green onions. Pour sauce over chicken.
Makes 4 to 6 servings.