Preheat the oven to 190°C/ 375°F. Prepare a lined baking tray.
Pat dry the chicken breast with a kitchen towel, season all over with salt and pepper. Whisk the egg in a medium bowl. Pour out the cornflakes onto a plate and crush using your hands. Dip the chicken breast in the egg wash, then coat all over in the cornflakes, press them in firmly to make sure they stick to the chicken. Transfer to the lined baking tray, spray all over with the cooking spray and bake for 20-25 minutes.
Mix the orange sauce ingredients, apart from the cornflour, in a bowl. Heat the oil in a pan or wok, sauté the garlic for 2-3 minutes over a medium heat, pour in the orange sauce and cook for 5 minutes over a low simmer. Stir in the cornflour and continue to cook the sauce over a medium heat, simmer and stir regularly until the sauce is thick and bubbling.
Bring a saucepan of water to the boil and steam the pak choi. Once the chicken is baked, drop them into the orange sauce and toss to coat. Serve immediately so the chicken is still crispy when you tuck in! Serve over white or brown rice, garnish with sesame seeds, spring onions and sriracha mayonnaise.
