Preheat your oven to 400°F and line a baking sheet with parchment paper.
In a shallow bowl, combine the buttermilk and mixed seasonings (garlic powder, paprika, salt, pepper). Add the chicken breast, ensuring it is thoroughly coated, and let it marinate for at least 30 minutes.
In another shallow dish, place the whole wheat breadcrumbs.
Remove the chicken from the marinade, allowing excess liquid to drip off, then dredge it in the breadcrumbs until evenly coated.
Place the coated chicken onto the prepared baking sheet.
In a mixing bowl, toss the broccoli with olive oil, a pinch of salt, and pepper until well-coated.
Arrange the broccoli around the chicken on the baking sheet.
Bake everything in the oven for 20-25 minutes or until the chicken is cooked through and the breadcrumbs are crispy, and the broccoli is tender with slight browning.
Remove from the oven, let the chicken rest for 5 minutes, then serve hot alongside the roasted broccoli.