To shell the fava beans and English peas, pinch the stem, pull the string, and open the pod along its seam to reveal the peas/beans inside. Bring a saucepan of water to a boil. Fill a medium bowl with ice water.
When the water has come to a boil, lightly salt it. Add the fava beans and English peas. Cook 2 minutes. Drain, and add to ice water. Drain.
Peel the fava beans by pinching the peel at one end so the emerald-green bean slides out.
Trim the sugar snap peas by pulling the stem to zip off the tough strings. Thinly slice them on the diagonal. Zest the lemon to equal 1 tsp, and juice the lemon.
In a medium bowl, whisk the lemon zest and juice, olive oil, garlic, salt and pepper. Add the English peas, sugar snap peas and fava beans, tossing to coat. Let stand 20 minutes. Taste again, and add more lemon juice, salt and/or pepper to taste. Stir in the mint. If desired, sprinkle with flake sea salt. (Makes 3½ cups.)