MIx all of the dressing ingredients in a bowl. Stir well and let it all sit while you work on the rest of the salad.
Steam or lightly cook your asparagus spears over simmering water. Don't overcook! They should remain bright green, so it only takes a minute or two!
Retrieving a grapefruit from its pithy coat may not be the fastest or easiest project, but it is worth it. While you can cut a grapefruit in half and retrieve the little bit as you would when you eat grapefruit out of its own bowl, I like the bigger pieces that you can get when going for the whole segment. To do this, peel your grapefruit. Remove as much of the bitter pithy parts as you can. Gently open it in half as you would when eating an orange. Now, remove the skin from each segment. Do this for most of the grapefruit segments, leaving 2 or 3 segments to squeeze into your dressing.
This salad is now mostly assembly. Place your greens/lettuce on the plates. Add your sliced avocado, grapefruit segments, and blueberries over the top. Slip in your avocado spears. Squeeze your remaining grapefuit juice into the dressing, stir well, and drizzle over the top, adding some of the slices of onions that are now deliciously marinated as well.