Preheat oven to 400 degrees F. Spray a large, rimmed baking sheet with non-stick cooking spray.
Prepare the sauce by combining all the ingredients in a large mixing bowl. Set aside.
Add the chicken pieces to a large mixing bowl. Pour the well-beaten egg over top and toss the chicken to coat.
In a separate large mixing bowl, add the panko breadcrumbs, all-purpose flour, one teaspoon of sea salt, pepper, and garlic powder. Whisk to combine.
Working in small batches, add the chicken pieces to the breadcrumb mixture and roll them around until each side is fully coated.
To one side of the baking sheet, add the chicken in a single layer.
Into a large mixing bowl, add the broccoli florets, mushrooms, and the bell pepper. Drizzle with one tablespoon of olive oil and season with sea salt, garlic powder, and black pepper. Toss to coat and place on the other side of the baking sheet.
Transfer the baking sheet to the oven and bake for 25 minutes, until the chicken is cooked through (165 F) and the vegetables are fork-tender and slightly browned.
Remove the pan from the oven and drizzle the prepared sauce over the chicken. Gently toss the chicken to coat each piece.
Sprinkle with sesame seeds and serve.