BLANCH: Bring a pot of salted water to the boil. Fill a large bowl halfway with ice, then top off with enough water to cover. Set aside. When the water is boiling, add the shrimp and cook until they’re opaque and hot all the way through, about a minute or so, depending on the size of the shrimp. Drain the shrimp and add them to the ice bath, stirring them through the water to make sure they’re covered.
SLICE: While the shrimp are cooling, prep the salad. Cut the top and bottom from each end of the oranges, then carefully slice off and discard the peel and pith. Thinly slice the oranges into slices. Thinly slice the red onion and layer the onion and orange slices in a platter or divide them between individual bowls.
SCOOP: Cut the avocados in half and remove the pits. Scoop out each half and cut them into four wedges. Add the avocado to the platter or bowls.
BLEND: Add all the vinaigrette ingredients to a high sided jar or cup. Use an immersion blender to blend until you have a smooth dressing. Taste and add salt, if needed.
SERVE: Drain and pat the shrimp dry, adding them to the platter or bowls. Drizzle the salad with the lemon basil vinaigrette and serve immediately. Garnish with additional fresh basil or Crispy Herbed Croutons, if you like.