1. Preheat the oven to 425 degrees Fahrenheit.
2. Coat the chicken with cornstarch, salt, and pepper (either shake it in a ziplock bag or toss it in a bowl). Set aside.
3. Spread the mixed vegetables and onion on a large sheet pan in a single layer. If they are piled too high, use two pans.
4. Toss the chicken stock, olive oil, tamari, maple syrup, garlic, ginger, and chile oil with the veggies (I like to do this with gloved hands to ensure even spreading).
5. Add the chicken to the pan, and gently toss it with the sauce, coating evenly.
6. Bake, uncovered, for 35 to 40 minutes or until the chicken is cooked through and the vegetables are tender and slightly browning on the edges. Check every now and again, and toss to ensure even cooking.