Place onion, jalapeno peppers, garlic, ginger, cumin, salt, coriander, cinnamon, and red pepper flakes in a large slow cooker. Pour in water and stir to combine. Mix in sweet potatoes, tomatoes, chickpeas, and peanut butter.
Set cooker to Medium-High, cover, and cook until sweet potatoes are tender and stew has thickened, about 6 hours. Stir in green beans, cover, and continue cooking until beans are heated through, 15 to 20 minutes.