Trim the woody stalks off the fennel bulb, then slice it thinly using a knife or mandolin.

Cut the ripe avocado in half, remove the pit, and scoop out the flesh. Slice into bite-sized chunks.

Peel the grapefruit and segment it by cutting between the membranes.

Rinse chosen lightweight greens gently and pat them dry. Tear into smaller pieces as necessary.

In a small bowl, whisk together grapefruit juice, olive oil, vinegar, shallot, mustard, salt, and pepper.

Drizzle the dressing over the salad ingredients and toss gently to combine.

Shave Parmesan-Reggiano cheese over the top of the salad and sprinkle with reserved fennel fronds.

Serve immediately on a platter or individual bowls.