In a medium bowl, whisk together mayonnaise, miracle whip and sugar, then season to taste with salt and black pepper.
To chop the iceberg lettuce, smash the stem of the lettuce on the counter to loosen it, then push it into the lettuce until it releases. Discard stem, then chop lettuce and place in a 9×13-inch baking dish.
Add thawed and drained peas, diced Swiss cheese and green onions, then pour dressing over mixture. Toss together until everything is evenly coated.
Top with bacon bits, then refrigerate until ready to serve. Cover with aluminum foil or plastic wrap if serving later.