Zest 1/2 grapefruit, then cut off outer peel and membrane from both grapefruit. Cut fruit into thin rounds, saving juice.
Combine zest, juice, oil, shallot, salt, and pepper in a bowl and stir to blend. Toss fava greens and sprigs with dressing.
Spoon greens onto plates and tuck grapefruit into salads. If you like, scatter flowers on top.
*Find at farmers' markets.
Note: Nutritional analysis is per serving.