Saute onion and garlic with olive oil over medium heat for about 3-4 minutes. Stir in cubed potato and zucchini. Cook for about 3-4 minutes stirring occasionally.
Add salt and vegetable stock. Simmer for about 15 minutes or until the potatoes soften.
Add spinach and cook for 2-3 minutes.
Blend until smooth with a hand blender.
Add lemon juice and serve into plates.
Pour a dollop of yoghurt, drizzle some olive oil and add a pinch of mint if desired.