Preheat the oven to 400°F and prepare a large (15×21-inch) sheet pan and an oven-safe cooling rack; spray the cooling rack generously with cooking spray.
Combine the dried parsley, Italian seasoning, garlic powder, paprika, 2 tsp salt, 1/2 tsp pepper, dried basil, and onion powder in a small bowl; remove 1 tablespoon of this spice mixture and set it aside for the zucchini.
Pat the chicken tenderloins dry, trim any fat and tendons, and set aside.
In a shallow bowl combine the panko and 1 cup (about 70 g) of grated Parmesan; toss and set aside.
In another large shallow bowl whisk together the mayonnaise, flour, egg, Dijon, and the remaining spice mixture to form a coating batter.
Using tongs, dip each chicken tender into the batter to coat evenly, then press into the panko-Parmesan mixture to fully bread each tender; place the breaded tenders on the sprayed cooling rack on the sheet pan. Press any extra breading onto the tops and spray the exposed side of the tenders with cooking spray.
Cut zucchini into 3-inch coins, halve each coin, then cut into wedges (about 4–6 wedges per coin). Spread zucchini on the sheet pan, drizzle with olive oil and the reserved 1 tablespoon spice mixture, and toss to coat. Move zucchini so there is room for the cooling rack with the chicken, arranging wedges in a single layer with space between pieces.
Bake in the center of the oven for 10 minutes, then carefully flip the chicken tenders, spray the top side with cooking spray, and bake another 5–10 minutes until the chicken reaches 160°F on an instant-read thermometer (carryover will bring it to 165°F) and the zucchini is crisp-tender.
While the pan finishes, whisk together the prepared coleslaw dressing, yellow mustard, and honey BBQ sauce in a small bowl until smooth.
Remove the cooling rack with chicken from the sheet pan. Sprinkle the remaining 1/4 cup Parmesan over the roasted zucchini and toss with any fallen panko crumbs. Serve the zucchini with the chicken tenders and the dipping sauce.