Put the beans and bay leaf in a large saucepan, add enough water to cover by 2 inches and bring to a boil. Simmer over low heat, stirring, until the beans are tender, 50 minutes; add water to maintain the water level. Remove from the heat and stir in 1 tablespoon of salt. Let stand for 5 minutes. Drain the beans, discard the bay leaf and let cool.
In a large pot of salted boiling water, cook the dandelion until tender, 4 minutes. Drain and let cool, then lightly squeeze out excess water. Coarsely chop the dandelion.
In a bowl, combine the oil, lemon zest, lemon juice and mint. In a large bowl, combine the beans and dandelion. Add the onion, olives and dressing; toss well. Season with salt and pepper and toss again. Cover and refrigerate for 1 hour. Serve lightly chilled.
The intense flavors of bitter greens make most wines seem astringent. But a zesty white with bright acidity like a Grüner Veltliner can actually makes the greens taste lively—almost like a squeeze of lemon.