In a large pot, cook the pasta according to the package directions. Drain, rinse with cold water to cool, and drain well again. Rinse the pot to cool, and then return the pasta to the pot. (Pasta may be prepared, tossed with a tablespoon of olive oil, and refrigerated until ready to use.)
Meanwhile, combine the mayonnaise, lemon juice, dill, garlic powder, salt and pepper in a small bowl. Stir until smooth. (Dressing may be prepared in advance, covered, and refrigerated until ready to use.)
To the cooled pasta, add the tomatoes and lettuce. Drizzle with about 3/4 of the dressing. Add the bacon and avocado, and toss to combine. Drizzle with more dressing, if desired, or reserve to add to any leftovers. The dressing also tastes great on steamed broccoli.