Put a large pot of lightly salted water on to boil.
Combine tuna, 1/3 cup red peppers, onion (or scallions) and capers in a large bowl.
Combine yogurt, basil, oil, lemon juice, garlic, salt, pepper and the remaining 1/3 cup red peppers in a blender or food processor. Puree until smooth.
Cook pasta until just tender, 10 to 14 minutes or according to package directions. Drain and rinse under cold water. Add to the tuna mixture along with the red pepper sauce; toss to coat.