Cook pasta to just barely al dente. Drain well, but do not rinse. Place hot, cooked pasta in a large bowl.
While pasta is cooking, prepare the celery and red onion. Mix the dressing by combining all the dressing ingredients and mixing well.
Add 2/3 of the dressing to the pasta, along with the tuna, red onion and celery. Mix well to combine. Allow to cool slightly, then cover well with plastic wrap and refrigerate until completely cool. Cover and refrigerate the remaining 1/3 of dressing, as well. Before serving, stir gently to loosen the pasta and stir in the remaining dressing. Season with salt and pepper, to taste.