Grapefruit, Walnut, and Feta Salad

Instead of grapefruit, you can use oranges or tangerines, and instead of feta - goat's cheese.
Peel the grapefruit and cut it into slices, put it in a bowl; squeeze the shells to squeeze out the juice. Set the pieces aside; reserve 3 tablespoons of juice. Remove the shells.Combine the juice, olive oil, sugar, salt and pepper, stirring with a whisk. Spread the lettuce leaves evenly over 4 plates; sprinkle each salad with 1 tablespoon of chopped feta cheese and 1 tablespoon of toasted walnuts. Spread the grapefruit slices evenly over the salads and drizzle with the vinaigrette.