Preheat oven to 350°.
In a medium saucepan, heat the olive oil. Add ginger, shallots, onions, garlic and sage leaves. Add the salt and pepper. Sauté until onions are translucent. Add the cinnamon and coconut milk. Bring to a boil.
In a medium shallow casserole dish, fan out red apple, fennel, green apple in that order. Follow the pattern until the dish is filled.
Pour the coconut milk mixture over the apples and fennel. Place casserole on the middle rack of the oven, and bake for 35-40 minutes. Allow the gratin to cool to room temperature and garnish with fresh sage before serving. Dig in!