Bring a large pot of lightly salted water to a boil. Cook pasta, stirring occasionally, until just tender, 8 to 10 minutes, or according to package directions. Drain and refresh under cold running water.
Whisk mayonnaise, yogurt, oil, vinegar (or lemon juice), garlic, salt and pepper in a large bowl until smooth. Add the pasta and toss to coat. Add tomatoes, bell pepper, carrots, scallions, olives and basil; toss to coat well.