Any assortment of fresh oranges and grapefruit will work well in this easy salad recipe. If you can't find one of each variety listed, you can use all navel oranges, or 3 navel oranges and 1 grapefruit.
Slice the ends off oranges and grapefruit so they stand upright. Cut off the remaining peel and white pith, following the curve of the fruit. Slice each crosswise into rounds; remove any seeds.
Whisk oil, lemon juice, honey, thyme, shallot, mustard, salt, and pepper in a small bowl.
Combine greens and radicchio. Arrange on a platter. Top the greens with the citrus slices and sprinkle with pomegranate seeds. Pass the dressing to serve.
To make ahead: Make the dressing up to 4 days ahead; refrigerate until ready to serve.