In a microwave-safe plate or bowl, add onions, carrots, celery, and red bell pepper. Cook in microwave for about 4 minutes until vegetables are softened.
Coat a large nonstick pan or soup pot with cooking spray. Add cooked vegetables, garlic, chili powder, and red pepper flakes. Sauté for about 1 minute. Stir often.
Stir in broth, chicken, and tomatoes. Bring to a boil, reduce heat to low, and simmer for 10 minutes.
Stir in peanut butter with a fork. Make sure the peanut butter gets well blended. Add couscous, spinach and mix well. Cover, remove from heat. Allow sitting 5 minutes.
To serve: Ladle 1¼ cups into each bowl. Garnish each serving with 1 tablespoon chopped scallions if desired.
This soup will keep in refrigerated for several days. Leftovers are wonderful for lunch. This soup freezes great, too!