In a large deep skillet, cook bacon over medium-high heat until evenly browned. Remove bacon to paper towels, and reserve drippings in the skillet.
Place fresh green beans in a large saucepan, and add enough water to cover the bottom by 1 inch. Cover, and bring to a boil over medium-high heat. Cook for 8 to 10 minutes, until bright green and tender. Drain.
Place the green beans into a 2 quart casserole dish. Spread the onions in a layer over the green beans. Place bacon strips in a layer over the onions. Sprinkle almonds over the top. Heat the reserved drippings in the skillet over medium heat. Stir in vinegar and sugar, heating just until sugar is dissolved; drizzle over everything in the dish. Cover, and chill for at least one hour, but overnight is best.
Preheat the oven to 350 degrees F (175 degrees C). Bake uncovered, for 45 minutes, until the onions are tender, and the almonds are toasted. Check after 30 minutes, and cover if necessary.