Boil a large pot of salted water and cook the rotini pasta according to package instructions for about 8-10 minutes until al dente. Drain and rinse under cold water.

In a skillet, heat olive oil over medium-high heat. Add ground beef and cook for 5-7 minutes, breaking it apart until browned. Drain excess fat and let cool.

In a large bowl, combine the cooled pasta, browned beef, cheddar cheese, tomatoes, and red onion. Toss gently to mix.

Drizzle Thousand Island dressing over the mix and fold gently to coat all ingredients without overmixing.

Cover with plastic wrap and refrigerate for at least 30 minutes before serving. Fold in chopped lettuce just before serving.