Wash lettuce and chop into strips, starting at root and working your way up. Coarsely chop a healthy amount of dill (enough so you have a third as much dill as lettuce). Chop the light green and white portions of the green onion. Slice the red onion into thin rings. Combine lettuce, dill, scallions, and about one-quarter cup of the thinly sliced red onion in a large salad bowl. Combine oil, vinegar, salt, and pepper and stir briskly with a wire whisk until combined. Taste to correct seasonings. Dress salad, add salt to taste, and toss. For added zip, top with a bit of crumbled blue cheese if desired, and serve immediately.