Bring a large pot of heavily salted water to a boil. Add 12 ounces dried pasta and cook according to package directions until just tender, 10 to 13 minutes. Place 1 cup frozen peas in a colander and set in the sink. Meanwhile, make the dressing and prepare the remaining ingredients.

Juice 1 medium lemon into a large bowl until you have 2 tablespoons. Add 3/4 cup plain Greek yogurt, 1/4 cup mayonnaise, 1 (1-ounce) envelope onion soup mix, 2 tablespoons water, and 3/4 teaspoon packed light or dark brown sugar. Stir to combine.

Prepare the following, adding each to the dressing as it is completed: Dice 1 small red onion until you have 1/2 cup. Dice 2 large celery stalks (about 1 cup). Halve 2 cups cherry or grape tomatoes (quarter if large). Stir to combine.

When the pasta is ready, drain directly over the peas and rinse with cold water to cool. Drain well. Add the pasta and peas to the dressing and toss to coat. Taste and season with kosher salt and black pepper as needed.

Thinly slice 1/2 small bunch fresh chives until you have 2 tablespoons. Garnish the pasta salad with the chives.