Boil 1/4 cup balsamic vinegar, 2 tablespoons brown sugar and the juice of 1 lemon in a saucepan until thickened, about 5 minutes. Whisk in 2/3 cup olive oil and season with salt and pepper. Combine torn frisee, romaine lettuce and red endive in a large bowl. Add sliced red onion, scallions, parsley and candied walnuts. Toss with the dressing.