HEAT a pot over medium. Add oil, then onion. Cook until soft, about 6 min. Add garlic and spices. Cook for 30 sec. Add tomatillos, breaking them up into chunks with a wooden spoon. Reduce heat to medium-low. Simmer for 5 min.
STIR in water and chicken. Increase heat to medium. Gently boil, stirring often, until chicken is cooked through, 7 to 8 min. Stir in beans and spinach until just wilted, about 1 min. Spoon into bowls and serve with desired toppings.