Halve the onion and cut into fine strips. Brush off the mushrooms and cut in half or in quarters depending on the size. Cut the chicken breast fillets into even strips or cubes and season with pepper.
Heat some oil in a pan and fry the meat in portions and then keep warm. Then fry the mushrooms and the onion strips briefly in the pan, deglaze with balsamic vinegar and honey, add the stock and simmer for about 2 minutes. Remove some of the liquid to thicken, stir it with the cornstarch until smooth and put it back in the pan. Season to taste with salt and pepper.
Finally, add the meat with the resulting gravy to the sauce and let it steep for a short time over a low heat.