Slice each pecan half into three lengthwise pieces. Mix together the cinnamon and brown sugar. Toss pecans with melted butter, then with the cinnamon/sugar mixture, tossing well to ensure a thorough coating. Put the nuts on a parchment-lined baking sheet and bake for 5 to 8 minutes, until sugar is caramelized. Remove the baking sheet from the oven, slide the parchment together with the nuts off the sheet to cool, and set aside.
Chop the lettuces into smallish bite-sized pieces; use a salad spinner to wash and dry them. Slice the green onion. Place the chopped lettuce in a large serving bowl (one large enough to toss the salad in). Add the vinaigrette and toss thoroughly to coat. Sprinkle with the chopped onion. Break the cooled pecan slices apart and sprinkle them over the salad.