Grill the onion: coat all sides of the onion with 1Tbl of the olive oil and cook over direct medium heat until tender; 8-12 minutes.
Toss the potatoes with remaining 2Tbl of oil, salt and pepper and grill 10-15 minutes. Potatoes should be crispy on the outside and tender inside.
Prepare dressing: Cook the bacon in a large skillot over medium heat and remove. Reserve 3 Tbl bacon dripings and discard overage. Sautee celery for three minutes. Add sugar and cook until sugar has dissolved and celery is cooked through: 2-3 minutes with an occasional stir. Add vinegar adn 1/2 cup water and cook until bubbling and slightly thickened. Reduce heat and add mustard, pepper and salt and cook an additional 2 minutes. Remove from heat, add the bacon pieces and onions, toassing to coat with dressing.
Cut grilled potatoes into bite-sized pieces and toss in a large mising bowl with the dressing. Add pickles and parsley. Toss gently and serve warm or at room temperature.