How to Make It
Preheat the oven to 400°. In a food processor, pulse the pretzels until coarsely ground; you should have coarse chunks and fine crumbs. Transfer to a large, shallow bowl.
Wipe out the food processor. Add the oil, whole-grain and Dijon mustards, water and vinegar and process until smooth. Season the dressing with salt and pepper.
Pour half of the dressing into a large shallow bowl, add the chicken breasts and turn to coat. Dredge the chicken in the pretzel crumbs and transfer to a rack set over a rimmed baking sheet. Bake in the upper third of the oven for 20 to 25 minutes, or until cooked through. Slice the chicken and serve warm or at room temperature with the remaining mustard dressing.
For a crisp topping, it's essential to use thick, hard pretzels, such as the sourdough or handmade versions.