Bring salted water to a boil and cook pasta until al dente.

Drain pasta and rinse with cold water.

Cook bacon until crispy and crumble into pieces.

Chop lettuce, halve tomatoes, and dice onion.

In a bowl whisk together mayonnaise, sour cream, lemon juice, mustard, garlic powder, salt, and pepper.

In a large bowl combine pasta, bacon, tomatoes, and onion.

Pour dressing over the pasta mixture and toss to coat.

Add chopped lettuce just before serving and mix gently.

Chill for 30 minutes if desired before serving.