Grilled shrimp on a salad of lentils and fresh herbs makes a light summer meal.
In a 3-quart saucepan, combine 4 cups water, lentils, garlic, bay leaf, cumin, andsalt and pepper to taste, and bring to a boil. Reduce heat and simmer until lentils are tender, about 30 minutes.
Meanwhile, with a sharp knife, remove peel and pith from fruit. Over a bowl, cut away membrane, collecting juice. Chop fruit into 1/4-inch dice; add to juice. Toss with1/2 tablespoon oil and season with salt and pepper. Set aside.
Cut cucumber on diagonal into 1/4-inch slices, then cut into thin strips. Set aside.
Drain lentils; discard garlic and bay leaf; let cool. Toss with onion, tomatoes, mint, parsley, watercress, lemon juice, vinegar, remaining oil, and salt and pepper to taste. Set aside.
Heat grill or cast-iron grill pan. Marinate shrimp for 10 minutes in 2 tablespoons of the citrus dressing. Remove shrimp, season with salt and pepper, and grill until opaque, about 3 to 4 minutes per side.
Divide the cucumbers among 4 plates. Top each with a quarter of the lentils and 3 shrimp. Spoon citrus dressing over salads.