1. Preheat the oven to 400 degrees F. Line 2 baking sheet with heavy-duty foil; place a cooling rack on one of the pans.
2. Pulse the pretzels in a food processor until finely ground. Pour the pretzel crumbs onto the baking sheet without the cooling rack. Add the panko and olive oil and stir to combine. Bake, stirring once, until the crumbs are slightly brown, about 5 minutes; allow the crumbs to cool.
3. Pour the flour onto a large piece of foil. Whisk together the buttermilk, 1/4 cup of the mustard, 1 teaspoon salt and 1/4 teaspoon pepper in a medium bowl. Sprinkle the chicken thighs on both sides with a pinch of salt and pepper. Set up a breading station, starting with the chicken and followed by the flour, the buttermilk mixture, the pretzel crumb mixture and the pan fitted with a rack.
4. Dredge each piece of chicken first in the flour, then in the buttermilk mixture and then in the pretzel crumb mixture, making sure to press the pretzel coating into the chicken; place the chicken pieces on the rack. Bake until the chicken is brown and crispy, about 35 minutes, flipping the pieces halfway through cooking. Let cool 10 minutes, flipping the pieces halfway through so they stay crisp on both sides.
5. While the chicken cooks, put the pineapple chunks with their syrup, the remaining heaping tablespoon Dijon mustard, 1/4 teaspoon salt and 1/4 teaspoon pepper in the bowl of a food processor and process until smooth. Transfer the mixture to a small saucepan and cook over medium heat until the sauce is slightly thickened and resembles apple sauce, about 5 minutes. Set aside to cool slightly.
6. Place the chicken on a serving platter along with the pineapple dipping sauce. Be sure to serve the chicken in one even layer so the breading does not steam. Sprinkle both the chicken and the sauce with the chopped chives.