Prepare an ice-water bath. Bring a saucepan of salted water to a boil. Cook fava beans until tender, 1 to 2 minutes. Drain, and transfer to ice-water bath. Let cool. Drain, and peel beans.
Pulse beans, goat cheese, oil, tarragon, lemon zest and juice, 1/2 teaspoon salt, and 1/4 teaspoon pepper in a food processor until just combined but still chunky, about 6 or 7 times. Stir in water. Add an additional tablespoon water if mixture is too thick. Transfer to a bowl. Refrigerate until ready to serve.
Sprinkle with pepper just before serving. Serve with radishes.
Delicious! Beautiful! I made this as an appetizer the other day. I write a blog called "Snippets of Thyme" (rileymadel.blogspot.com) and I wrote a feature article about your spread. The colors are soft but with the pop of red in the radishes it all comes together for spring.