Step 1

Bring a large pot of water to a boil. Add pasta; cook according to package directions. During the last minute of cooking, add peas.

Step 2

Meanwhile, place garlic in a medium bowl; sprinkle with salt and mash with the back of a fork into a chunky paste. Add buttermilk, mayonnaise, chives and vinegar; whisk until combined.

Step 3

Drain the pasta and peas and transfer to a large bowl. Add half the dressing and toss to combine. Cool to room temperature, tossing occasionally, about 10 minutes.

Step 4

Add summer squash, tuna, Parmesan, sun-dried tomatoes and the remaining dressing to the pasta mixture; mix until well combined.