In a medium saucepan, cover the grain of choice with 2 inches of water. Bring to a boil, cover and simmer over moderately low heat until tender, about 25 minutes. Drain and let cool for about 10 minutes.
Finely grate 1 tsp. zest from 1 orange; set aside. Using a sharp knife cut all peel and white pith from all 2 oranges. Cut between membranes to release segments into a medium bowl; discard membranes.
In a bowl whisk together zest, lemon juice, vinegar, garlic, oil, salt and fennel fronds.
Toss the grains, citrus, fennel and nuts (if using). Add vinaigrette and toss again.