Place beans in a bowl, cover with water by a few inches, and soak overnight. Heat 1/4 cup of the oil in a saucepan, add the onions and saute until soft and just golden, 5 to 7 minutes. Add 2 cups of water and bring to a boil. Drain the beans and add them to the saucepan. Cook over low heat until beans are very soft, adding more water if needed, about 1 to 1 1/2 hours. (There should hardly be any liquid left when the beans are ready.)

Meanwhile, roast bell peppers over a gas flame or on a tray under the broiler. Keep turning so the skin is evenly charred, without burning and drying out the flesh. Transfer charred peppers to a plastic bag, tie the top closed and let steam until cool to the touch, about 15 minutes. To peel peppers, pull off the charred skin by hand and then dip the peppers briefly in water to remove any blackened bits. (Do not peel the peppers under running water since that would wash away the flavorful juices.) Once peeled, cut away stems, seeds and veins, and slice peppers into strips.

Heat a grill. In a small bowl, combine the oregano, olive oil, vinegar, and salt and pepper.

Cut six 12-inch squares of aluminum foil. Divide pepper strips among center of foil squares. Arrange one feta square atop peppers, along with tomato slices, and drizzle reserved olive oil mixture over the top. Wrap foil packets securely and place on grill or under the broiler. Grill until packets are heated through, about 5 minutes.

When beans are ready, mash them with the back of a spoon to form a paste, or place in a blender and process until smooth. Stir in the remaining 1 tablespoon olive oil. Season with the lemon juice, sugar, and salt and pepper.

Spoon bean puree onto individual plates, and use a spatula to slip roasted peppers, feta and tomatoes off of foil and onto puree. Drizzle with olive oil, garnish with Kalamata olives, and serve with Retsina.