How to Make It
In a food processor, combine the 1/4 cup of olive oil with the tuna, lemon juice, anchovies, capers and mayonnaise. Process until smooth. Scrape the tonnato sauce into a serving bowl, cover and refrigerate.
In a pot of boiling salted water, cook the beans until crisp-tender, 2 minutes. Drain and rinse under cold water; pat dry.
Arrange the beans, carrots, celery, cucumbers, radishes and fennel on a platter; sprinkle with the sea salt. Drizzle the tonnato with olive oil; serve with the vegetables.