Notes: Up to 1 day ahead, cook beans, drain and immerse in ice water; when cold, drain airtight. Reheat in boiling water 2 to 3 minutes.
In a 5- to 6-quart pan over high heat, bring about 3 quarts water to a boil. Add beans. Stir occasionally until tender-crisp to bite, 4 to 5 minutes. Drain.
In a large bowl, combine oil, lemon peel, lemon juice, parsley, and garlic. Add beans and mix to coat. Add salt and pepper to taste. Pour into a serving dish and garnish with lemon slices.