1. Finely chop the onion (about 1 cup). Heat the olive oil in a large skillet over medium heat until hot. Reduce the heat to medium low; add the onions and cook for 5 minutes, or until it has softened. Press the garlic (about 1 tablespoon) into the pan and cook for 1 minute more.
2. Turn the heat up to medium-high. Add the ground chuck and cook, stirring and breaking up the lumps, for about 5 minutes, or until it is no longer pink.
3. Drain the chiles; finely chop the olives (about ¾ cup). Add 1 cup water, the chili sauce, chiles, olives, prunes, 1 teaspoon salt, and ¼ teaspoon pepper to the skillet; simmer for 10 minutes, or until most of the liquid has evaporated. Stir in the lemon juice, hot sauce to taste and salt and pepper to taste. Divide the mixture among the buns and serve.