In a large pot, combine the peanut butter, broth, diced tomatoes, onion, garlic, ginger, cayenne, cumin, salt, and pepper.
Bring the mixture to a simmer and cook for 15-20 minutes, stirring occasionally, until the flavors have melded.
Use an immersion blender to puree the soup until smooth and creamy.
Stir in the cooked chicken, if using.
Serve the soup hot, garnished with chopped cilantro.
