Step 1: Cook Pasta. Bring a large pot of salted water to a boiling point. Add pasta and cook until al dente, about 10 minutes. Add corn during the last 2-3 minutes. Drain and cool under cold running water.

Step 2: Prep Vegetables. Halve the cherry tomatoes, dice avocado, and slice spring onion. Place in a large bowl.

Step 3: Flake Tuna. Drain canned tuna and flake it into the vegetable bowl.

Step 4: Make Dressing. In a small bowl, whisk together mayonnaise, sour cream, mustard, lemon juice and zest. Mix in parsley and season with salt and pepper.

Step 5: Combine Ingredients. Add cooled pasta and corn to the vegetable-tuna mix. Fold everything together gently.

Step 6: Toss & Serve. Before serving, gently toss the salad again. Optionally, add avocado right before serving.