Cook the Pasta: Cook the gluten-free rotini pasta according to the package instructions. After cooking, drain and rinse under cold water to stop the cooking process. Set aside to cool.
Make the Dressing: In a medium bowl, whisk together the Greek yogurt, lemon juice, olive oil, oregano, minced garlic, dried dill, salt, pepper, and crushed red pepper flakes until smooth. Adjust seasonings to taste.
Prep the Vegetables: Chop the bell peppers, cucumber, grape tomatoes, and red onion. Slice the black olives and crumble the feta cheese.
Assemble the Salad: In a large bowl, combine the cooked and cooled pasta with the prepared vegetables, black olives, and feta cheese.
Add the Dressing: Pour the creamy dressing over the pasta and vegetables. Toss gently to coat everything evenly.
Garnish and Serve: Garnish with fresh dill or oregano, if desired. Serve chilled or at room temperature.