In a large frying pan, saute onions in olive oil just until tender. Add green beans, water, salt, and pepper and allow to come to a boil. Reduce heat and cover. Allow to simmer for five minutes or until beans are tender. If there is excess liquid in the pan, remove cover and raise heat until liquid has evaporated.
Transfer beans and onions to a serving bowl and drizzle with balsamic vinegar. Sprinkle with toasted almonds.
Serve warm or chill.