In a large bowl, combine the mustard, vinegar, sugar and 3 tablespoons of the oil. Add the onion, cabbage, lettuce, tomatoes and pickles and toss. Season the salad with salt and pepper; taste, adjust the seasonings and reserve.
Heat a large nonstick skillet over medium-high heat. Add the remaining 1 tablespoon of oil, 1 turn of the pan, then arrange the sliced dogs in a single layer. Sear them for a couple of minutes on each side, turning with tongs.
Mound the salad on plates, top with the seared dogs and serve.