Chicken Salad with Crème Fraîche and Rye

Preheat oven to 425 °. Place chicken on a small rimmed baking sheet and rub with 1 tablespoon oil; season with kosher salt and pepper. Roast until golden brown and cooked through, 25-30 minutes. Let cool, then shred into bite-size pieces. If using fresh fava beans, cook in a large saucepan of boiling salted water until tender, about 4 minutes. Drain and transfer to a bowl of ice water. Drain and peel. (If using frozen fava beans, cook 2 minutes; transfer to a bowl of ice water, then drain.) Toss in a large bowl with fennel, scallion, tarragon, vinegar, chicken, and remaining 3 tablespoons oil; season with kosher salt, pepper, and more vinegar, if desired. Meanwhile, whisk crème fraîche in a medium bowl to soft peaks (it will look fluffy); season with kosher salt. Toss cucumber with parsley, lemon zest, and lemon juice in a small bowl; season with kosher salt and pepper. Serve chicken salad with bread, cucumber, and a dollop of crème fraîche, topped with sea salt and more pepper. Do ahead: Chicken can be cooked 2 days ahead; cover and chill. Shred just before using. Fava beans can be cooked 2 days ahead; cover and chill.