Crush the pretzels. Pulse 3 cups of salted pretzels in a food processor until they reach a coarse, sandy texture (or place them in a zip-top bag and crush with a rolling pin). Transfer to a shallow bowl.
Set up the dredging station. In a second shallow bowl, whisk together the flour, garlic powder, smoked paprika, salt, and pepper. In a third bowl, whisk together the egg, mayonnaise, and Dijon mustard until smooth.
Bread the chicken. Pat the chicken tenders dry with paper towels. Working one at a time, dredge each tender in the seasoned flour (shake off excess), dip into the egg mixture (let excess drip off), then press firmly into the crushed pretzels, coating both sides. Press the crumbs onto the surface so they stick.
Rest the tenders. Place breaded tenders on a plate or rack and let them rest for 5 minutes while you preheat the air fryer. This step helps the coating set.
Preheat the air fryer to 400°F (200°C) for 3–5 minutes.
Air fry. Lightly spray the air fryer basket with oil. Arrange the tenders in a single layer with space between each — work in batches if needed. Spray the tops generously with oil. Air fry at 400°F for 5–6 minutes, flip, spray the other side with oil, then cook another 5–6 minutes, until the internal temperature reaches 165°F (74°C) and the coating is deep golden brown.
Make the honey mustard. While the chicken cooks, whisk together the Dijon, honey, and mayonnaise in a small bowl until smooth.
Rest and serve. Let the tenders rest for 2 minutes, then serve hot with honey mustard for dipping.