In a small pot, bring the white wine vinegar, water and cinnamon stick to a boil. Add in the shallot, jalapenos, and sugar, and then remove the pot from the heat. Adjust the seasonings with salt, if desired, and let the mixture set for 10 minutes.
Discard the cinnamon stick, and strain the liquid, reserving the pickled shallots, and jalapenos for the Plantain Gratin, recipe follows.
Preheat the broiler.
Place the plantains in a baking dish, and drizzle them with the vegetable oil, and season with salt to taste.
Broil the plantains for 5 to 7 minutes, or until they are slightly caramelized. Sprinkle the cheese and green onions over the plantains and continue broiling for 3 to 4 minutes, or until the cheese melts.
Transfer the plantains to a serving dish and garnish with the Pickled Topping and fresh cilantro leaves.