Preheat the oven to 350°F (or 180°C).
Peel and cut the potatoes. Boil them until they become tender.
Blend cashew nuts together with soymilk and vegetable broth, then add the potatoes and blend it all together. Add salt and stir well. The consistency should be soft but firm.
Grind the chickpeas together with the garlic cloves, parsley and a little salt in a processor. A firm mash must also be obtained
Sauté the leeks, celery and pepper with some water or vegetable broth. Add spinach and ginger. Cook a few more minutes. Add salt to taste.
Spray a baking dish with oil or cover the dish with parchment paper. Spread the mashed chickpeas on the bottom of the baking dish. Then, layer with the put the spinach filling. Finally, add the top layer of mashed potatoes, covering the filling very well.
Bake for 30 minutes.