Bring 4 quarts of water to a boil in a large pot; add 1 tablespoon salt and the elbow pasta.
Cook the pasta until al dente, about 6–8 minutes, then drain in a colander.
Rinse the drained pasta with cold water until it is no longer hot, then drain briefly, leaving a little moisture.
Transfer the pasta to a large bowl and add the minced red onion, minced celery, chopped parsley, lemon juice, Dijon mustard, garlic powder, and cayenne pepper; stir to combine and let sit 2 minutes.
Add the mayonnaise and stir until evenly coated; let the salad rest 5–10 minutes for flavors to meld.
Season to taste with salt and pepper, then serve immediately or chill as desired.