Boil the pasta according to package directions until all the way done. Drain and run cold water over the pasta. Set aside.
Cut the cherry tomatoes, cucumber, red onion, and green pepper and set aside.
Dressing: In a medium bowl, combine the mayo, Hiland Buttermilk, lemon juice, lemon zest, garlic powder, red pepper flakes, salt, and pepper. Whisk together until smooth. Taste and adjust if more salt is needed.
In a large bowl, add the cooked and cooled pasta, the veggies, and pour the dressing over top. Mix and combine together so that all the pasta and veggies are coated in the dressing.
Add the feta cheese and walnuts to the top and combine again. Serve!