Bring a large pot of lightly salted water to a boil. Place pasta in the pot, cook for 8 to 10 minutes, until al dente, and drain. Rinse under cold running water to cool.
Place bacon in a skillet over medium high heat, and cook until evenly brown. Drain and crumble.
In a large bowl, gently toss together the pasta, bacon, shrimp, avocados, Cheddar cheese, mayonnaise, lemon juice, tomatoes, and red pepper. Serve over lettuce.