To make the cashew ricotta, place the chopped onion, water, sugar and salt in a small saucepan and cook over low to medium heat, stirring occasionally, for around fifteen minutes or until the water has cooked away and the onions are soft and sweet.
Meanwhile, drain and rise the soaked cashews and place them, the milk, garlic powder and lemon juice in a blender and blend until well combined and smooth. The cashews will still have a little texture. Add more milk one teaspoon at a time if needed to get the mixture moving. Place the "ricotta" in a bowl before adding the onion and stirring through. Set aside.
Pre-heat the oven to 180 degrees C and line two baking trays with parchment. Brush each eggplant with olive oil on both sides and place them on the trays. Place in the oven for seven minutes before turning each eggplant slice over and cooking for another ten minutes. The eggplant should be pliable to roll but not overcooked.
While the eggplant is cooking, heat the oil for the tomato sauce in a small saucepan before sautéing the garlic for a minute. Add the cherry tomatoes and cook for two minutes before adding the spinach, basil and lemon zest. Continue cooking, stirring regularly, for around ten minutes. Add sea salt to taste.
Once the eggplant is cooked, remove them from the oven and allow to cook slightly. Leave the oven on at 180 degrees C.
Set up an assembly line on your kitchen counter starting with the tomato sauce, followed by the eggplant, zucchini ribbons and finally the cashew ricotta. Place an oven-proof baking tray or skillet near you.
To assemble to involtini, spoon enough tomato sauce to cover the bottom of your pan. On a board or plate, lay a slice of eggplant down followed by overlapping ribbons of the zucchini (I use enough zucchini to match the width of the eggplant). Spoon around a tablespoon of the cashew cheese on to the zucchini on the end closest to you before rolling the stack gently away from you. Place the roll down on to the tomato sauce with the seem down to keep the roll in place. Repeat with remaining eggplant slices.
Spoon any remaining tomato sauce in between and in the centre of the rolls before drizzling with olive oil and adding a pinch of sea salt. Bake in the oven for 25 minutes.
Remove from the oven and serve hot.