In a large, thick-bottomed pot over medium-high heat, add the olive oil. When the oil is hot (but not smoking) add the garlic and onions and saute for a few minutes along with pinch of salt - just until they soften up a bit. Stir in the potatoes and zucchini. Add the stock. Bring to a simmer and cook until potatoes are soft throughout, roughly 10-15 minutes.
Stir in the spinach, and wait for it to wilt, just ten seconds or so. Now stir in the cilantro. Puree with a hand blender until smooth. Whisk in a big squeeze of lemon juice. Now taste, and add more salt if needed. Finish with a drizzle of olive oil and serve.