1. Spray a large pot or Dutch oven with vegetable cooking spray. Heat pot over medium-high heat. Add chicken. Cook, stirring constantly, until cooked through and no longer pink, about 10 minutes. Place chicken on a plate. Set aside.
2. Spray same pot with more vegetable cooking spray. Add onion. Cook, stirring frequently, until softened, about 5 minutes.
3. Add sweet potatoes, broth, 1 cup water, and nutmeg to pot. Bring mixture to a boil over high heat. Reduce heat to low; cover and simmer until sweet potatoes are tender, about 15 minutes.
4. In a small bowl, combine flour and remaining water. Stir flour mixture into pot. Bring to a boil over high heat. Cook, stirring constantly, until mixture thickens, about 5 minutes. Stir in chicken and spinach. Cook, stirring, until stew is heated through, about 10 minutes. Serve immediately.