Slice the tops and bottoms from the grapefruit and oranges. Using a paring knife, cut away the skin, including the pith, from the citrus to reveal the flesh. Place the citrus on it’s side, and working from the top (or bottom) end, cut thin slices. Lay the citrus slices in a single row on your cutting board or another flat surface and sprinkle with salt. Set aside to allow the salt to work into the citrus while you prepare the rest of the salad, about 15-20 minutes.
Prepare the vinaigrette. Zest the orange, then slice in half and juice into a small bowl. To the bowl, add the champagne vinegar, salt, and pepper. Whisk until combined. Slowly pour in the olive oil and whisk until emulsified.
Using your paring knife, peel the jicama and slice in half. Set one half aside for another purpose. Slice the other half into quarters, and then julienne using a sharp knife or mandoline slicer.
In a salad bowl, add the baby kale, jicama, parsley, and half the vinaigrette, then toss to combine. Transfer the dressed salad to a platter, or divide between four plates. Top the salad with the salted citrus slices and sliced avocado. Serve with additional dressing to taste. Serve immediately. The salad base and oranges can be stored separately in the fridge in a sealed container for up to 24 hours.