Bring a big pot of salted water to a boil.

Place the garlic cloves on a cutting board. Crush with the flat side of a knife. Continue crushing and chopping until you have a garlic paste. Transfer garlic paste to a small bowl, add harissa paste, and olive oil.

Add the spaghetti to the boiling water and cook according to package instructions. Just before the pasta is done add the spinach to the pasta water, count to the count of 10, drain, and set aside.

Heat the harissa sauce over medium heat in the pot, add spaghetti and spinach, black olives, pine nuts, and lemon zest. Add a little pasta water to help make the sauce. Stir over the heat for a minute or so, then turn everything out onto a platter and serve.