Cook the Shrimp
In a medium pot, bring salted water to a simmer. Slice one lemon and add it along with the shrimp to the pot. Simmer gently, avoiding a rolling boil, until the shrimp become opaque, typically 2 to 4 minutes depending on size. Once cooked, drain the shrimp and discard the lemon slices. You may opt to chop the shrimp into smaller pieces if preferred.
Prepare the Dressing
Zest the remaining lemon and place the zest into a large bowl. Cut the lemon in half, squeeze the juice into the bowl, and then whisk in the mayonnaise and olive oil until the dressing is smooth and well-combined.
Assemble the Salad
To the bowl with the dressing, add the cooked shrimp, diced celery, red onion, and chopped herbs. Toss everything together to combine, seasoning with salt and pepper to taste. Cover the salad and refrigerate until ready to serve. If desired, serve on a bed of lettuce and avocado, or alongside other vegetables for a more filling meal.