Cook pasta according to package directions, omitting salt and fat. Drain pasta in a large colander over a bowl, reserving 1/2 cup cooking liquid. Rinse pasta under cold water; drain. Drain tuna, reserving 2 tablespoons oil. Grate 2 teaspoons rind from lemon; squeeze 3 tablespoons juice. Combine reserved oil, rind, and juice in a large bowl; stir with a whisk. Add pasta to oil mixture, tossing to coat. Fold in tuna and apple. Remove fronds from fennel bulb; finely chop fronds to measure 3 tablespoons. Remove and discard stalks. Thinly slice fennel bulb. Stir fronds and sliced fennel into pasta mixture. Add reserved pasta liquid and 1/2 teaspoon salt, tossing to coat pasta salad evenly.

Sustainable Choice: Industry label regulations require solid white tuna to be from the albacore variety.