Start by slicing the meat and veggies into thin, bite-size pieces.
In a large pan, add 1 tbsp of olive oil and set it over medium-high heat.
Melt 1 tbsp of butter and then add 1 tbsp of soy sauce to that same pan, then the chicken and season it using salt and pepper to taste. Make sure to stir it often. Once it’s properly cooked, set it aside and cover it with some foil.
Using the same skillet, add 1 tbsp of butter, 2 tbsp of soy sauce, and all the veggies (onions, zucchini, broccoli), together with salt and pepper to taste. Cook until they’re tender enough to be pinched using a fork, so about 7 to 8 minutes.
Then add the chicken and mushrooms back into that same skillet, together with the vegetables.
Add an extra tablespoon of butter and the last tablespoon of soy sauce and finish cooking them until the mushrooms are tender and the chicken is properly heated throughout.
If necessary, add more salt and pepper and then toss in a little lemon juice right before serving.