Fennel, Grapefruit, and Arugula Salad

I first tasted grapefruit and fennel together in a salad at a pizzeria and instantly fell in love with the idea. I kept making different versions of it over the years and the one below is now my general go-to recipe, though I often add beets as well. You can take this basic idea and come up with variations depending on your fancy or whatever happens to look good in the market that day.

• 4 cups fresh arugula
• 1 small bulb fennel, or 1/2 of a large bulb of fennel
• 1 medium grapefruit, ruby red or pink, cut into segments and juice retained
• 1 small avocado, ripe
• 1 scallion, dark green part only
• 1/4 cup extra-virgin olive oil
• 1 dash fine sea salt, or to taste
• 1 dash freshly ground black pepper, or to taste