Cut off the tips on the bananas and make a lengthwise slit from one end to the other. These will be boiled whole, peel and all. When done, the peel should slide right off. No peeling!
Note, while the bananas boil prepare the sauce.
In a large pot, bring up at least two quarts of salted water to a boil. Add the green bananas and allow to cook until they can be easily pierced with a paring knife (about twenty minutes). Drain them and let cool until easy to handle. Slice the guineos into one-inch rounds.
In a medium caldero heat the olive oil over medium heat. When the oil is hot, add the onions and the garlic, and sautée until soft, about ten minutes. Add the vinegar, bay leaf and peppercorns and allow this mixture to simmer on low heat for twenty minutes.
Let the pickling liquid cool until it reaches room temperature, and pour over the room temperature bananas.
Store in a glass container. Refrigerate for at least an hour before serving. Best if made one day ahead.