In medium bowl, mix sauce ingredients. Refrigerate until serving time.
In 10-inch nonstick skillet, heat oil over medium heat. Add onion; cook about 5 minutes, stirring occasionally, until translucent. Add garlic; cook, stirring frequently, until softened. Stir in curry powder, turmeric, cinnamon and red pepper; cook and stir about 30 seconds.
Spray 3- or 4-quart slow cooker with cooking spray. In cooker, mix onion mixture and remaining curry ingredients except spinach and couscous.
Cover; cook on Low heat setting 5 to 6 hours.
Stir spinach into curry in cooker. Cover; cook on Low heat setting 5 to 10 minutes longer or until slightly wilted.
Meanwhile, cook couscous as directed on package. Serve curry over couscous; top with sauce.