Step 1

Cook pasta according to package directions, omitting salt. Drain and rinse under cold water until cool. Transfer to a large bowl.

Step 2

Shred tuna into medium-size chunks in a medium bowl.

Step 3

Add celery, bell pepper, scallions, yogurt, mayonnaise, dill, lemon juice, mustard, salt and pepper to the pasta; stir until well combined. Gently fold in the tuna until just incorporated, leaving some chunks intact and being careful not to overmix. Garnish with additional scallions, if desired.