Preheat the oven to 450 degrees Fahrenheit and line a medium baking sheet with parchment paper.
In a medium bowl, beat the egg white with a whisk until fluffy. Add the chicken and toss to coat with the egg white. Sprinkle with 3 tbsp of the cornstarch and toss to coat the chicken with the cornstarch.
Spread the coated chicken in a single even layer on the prepared baking sheet and spray with a little bit of avocado oil spray. Bake for 10 minutes, then flip the chicken. Bake for another 2-3 minutes or until the chicken is cooked through.
Meanwhile, to a small saucepan, add the soy sauce, orange juice, honey, maple syrup, balsamic vinegar, miso paste, sesame oil, red pepper flakes, ginger, and garlic. Stir to combine and bring to a low boil. Reduce the heat and simmer for about 5 minutes, stirring often, until slightly thickened and reduced. Stir in the remaining ½ tbsp cornstarch and simmer another minute, stirring often until thickened.
Change the oven to broil. Pour the sauce over the chicken on the baking sheet and toss, then return to the oven. Broil for about 3 minutes, tossing every minute, checking to ensure the sauce doesn’t burn. Remove from the oven and top with chopped green onion and sesame seeds to serve!