Spinach and watercress, abundant in antioxidants, are no chore to eat when blended into this healthful yet indulgent take on spinach dip. Avocado lends it richness, and colorful crudites add crunch but not empty calories.
Heat oil in a large skillet over medium heat. Add onion, and cook until softened, about 8 minutes. Reduce heat to medium-low, add garlic, and cook, stirring occasionally, until onion and garlic are very soft and golden, about 20 minutes. Add spinach, and cook, tossing often, until wilted, about 4 minutes. Let cool slightly.
Puree mixture in a food processor until smooth. Add watercress, avocado, yogurt, lemon zest and juice, hot sauce, and salt, and season with pepper. Puree until smooth. Transfer to a bowl, cover, and refrigerate for at least 1 hour (or up to 3 days). Stir the dip, and serve with crudites.