A stripped-down dressing of lemon juice and olive oil is all that’s needed for this salad, where smoked fish is the featured player. This most basic combination of fat and acid carries the trout’s gentle smokiness to every corner of the dish. And when the acidic sting of grapefruit (at Gjelina, we’re fools for the ones from Shaner Farms), lush slices of avocado, and the peppery bite of arugula come into play, this simple salad rises to the level of a classic.
Other citrus, such as orange or tangerine, works well here, too, but I think the intense acidity and floral qualities of grapefruit, and its cousins pomelo and oro blanco, are ideal.
Put the arugula in a large mixing bowl. Break up the trout into small chunks over the arugula. Drizzle with the lemon juice and olive oil and season with salt and pepper.
Add the grapefruit sections, avocado, and onion and toss gently, taking care not to break up the avocado slices while distributing them evenly throughout the salad. Transfer to a serving platter or individual plates and serve immediately.