Heat oil in a large pot over medium heat. Add onion and garlic, cooking for 2-3 minutes until tender. Add split peas and stock. Bring to the boil, then reduce to a simmer for 25 minutes until peas are tender.
Add zucchini and continue cooking for 10 minutes until cooked through. Stir in spinach and remove from heat. Puree soup until smooth and season to taste. Add additional water to adjust consistency if desired.
PESTO: Combine all ingredients in a small food processor or blender and process until a chunky pesto has formed. Set aside until required.
Serve soup with a drizzle of pesto.