Bring a large pot of salted water to a boil and set a bowl of ice water nearby. Drop the green beans into the boiling water and blanch for 2 minutes. Remove the beans and immediately immerse in the ice water long enough to cool completely, about 15 seconds. Drain and place on paper towels to dry.
Transfer the beans to a bowl and toss with the radicchio, onion, and a few spoonfuls of the dressing.
Arrange on a platter and top with small dollops of goat cheese, the walnuts, almonds, and tarragon. Drizzle with more dressing, season to taste with flaky salt, and serve.
