Prepare the dressing by stirring or whisking together the mayonnaise, lemon juice, Old Bay Seasoning, salt, black pepper, garlic powder, sugar, and dill in a medium bowl. Cover with plastic wrap and refrigerate.
Begin cooking the pasta according to package directions. Once the pasta has cooked, drain in a colander and rinse well with cold water until all of the pasta has cooled.
While the pasta is cooking, chop the vegetables and slice the imitation crab meat into bite-size pieces (about 1 inch).
Toss together the imitation crab, celery, red onion, bell pepper, and peas in a very large mixing bowl. Add the drained and cooled pasta and toss again to combine.
Add the dressing to the pasta mixture and gently stir to coat as evenly as possible.
Cover and refrigerate at least 1 hour before serving. Stir before serving to redistribute the dressing.