Preheat oven to 180C. Season duck to taste, place in a cold frying pan skin-side down and place over medium-high heat. Cook until skin is golden and fat is rendered (10-12 minutes). Turn then place in oven and roast until golden and cooked through (8-10 minutes). Cover with foil and set aside to rest (5 minutes).
Blanch leeks until tender (2-3 minutes), refresh and drain. Cut into bite-sized pieces and place in a large bowl. Add remaining ingredients and set aside.
For bacon vinaigrette, heat olive oil in a frying pan over medium heat, add bacon and cook until golden and crisp (2-3 minutes). Drain on absorbent paper. Add extra-virgin olive oil, vinegar and mustard to pan, whisk to combine, season to taste, add bacon and keep warm.
Thinly slice duck, add to salad, pour in vinaigrette, toss to combine and serve.