Preheat the oven to 450°F. Wash and dry the fresh produce. Halve and peel the onion; cut into ½-inch wide wedges. Cut off and discard the bottom ½ inch of the broccoli stem; cut the broccoli into small florets. Medium dice the potatoes. In a bowl, combine the mayonnaise and as much of the yuzu kosho as you'd like, depending on how spicy you'd like the dish to be; season with salt and pepper.
Line two sheet pans with foil. Pat the chicken dry with paper towels; season with salt and pepper on both sides. Place on one sheet pan. Transfer half the yuzu mayo to a separate bowl and set aside for serving. Evenly top the seasoned chicken with the remaining yuzu mayo, breadcrumbs (pressing gently to adhere), and sesame seeds. Drizzle with olive oil. Roast 18 to 20 minutes, or until the chicken is lightly browned and cooked through. Remove from the oven.
Meanwhile, place the onion wedges, broccoli florets, and diced potatoes on the remaining sheet pan; drizzle with the sesame oil and season with salt and pepper. Toss to coat and arrange in an even layer. Roast 20 to 24 minutes, or until tender when pierced with a fork. Transfer to a large bowl; add the togarashi and stir to coat. Serve the roasted chicken with the finished vegetables. Top the chicken with the reserved yuzu mayo. Enjoy!
