In a large nonstick pan, heat 1 tablespoon of oil on high heat. Add the onions and cook for about 2 minutes, then add the mushrooms. Cook for 2 minutes, then lower heat to medium high and add garlic, cooking for a minute. Season with ¼ teaspoon salt, ¼ teaspoon pepper, and 1 teaspoon garlic herb seasoning. Remove from pan.
Cut each chicken breast in half, so you end up with 4 skinny chicken breasts. Season both sides with ½ teaspoon salt, ¼ teaspoon pepper, and 1 teaspoon italian seasoning.
In the same pan, heat 2 tablespoons olive oil on high heat. Place the chicken and cook for 1 minute on each side. Do not move it around (only move when flipping). Add the cooked mushrooms and onions with the balsamic vinegar, honey, italian seasoning, oregano, and remaining salt, pepper, and garlic herb seasoning. Cook for 2-5 minutes (depending on how thick the chicken is), then remove the chicken. Do not remove the chicken until the internal temperature is 165 degrees Fahrenheit. Keep cooking everything else until the sauce thickens slightly, or to preference. Remove from pan and serve.