1. Preheat oven to 400°F. Make sure pretzel pieces are ground into fine small chunks/crumbs. You can do this in a food processor or by placing in a Ziploc bag and rolling aggressively with a rolling pin. Place pretzel pices in a shallow bowl.
2. Wisk together oil, mustard, water and vinegar until smooth. Add salt and pepper to taste.
3. Pour half the dressing into a shallow bowl (reserve remaining sauce for dipping later). Add chicken breasts, coating all sides.
4. Remove chicken from the dressing and place in pretzel bowl, coating all sides.
5. Place chicken on a baking sheet and cook 30 minutes, or until internal temperature reaches 165°F.
6. Serve warm or at room temperature with remaining dipping sauce.