Melt butter in a large frypan over medium-high heat. Add the cubed chicken and cook just until it turns white on the outside. Add the onion, garlic and mushrooms. Saute until onions begin to turn clear.
Pour in just enough Italian dressing to coat the chicken mixture then add 1 tablespoon of lemon juice. Cover and reduce heat to low then simmer while you make the sauce.
Combine cream of chicken soup with milk in a small saucepan over medium heat. Heat through but do not allow it to boil.
When the mixture is thoroughly heated stir in 4 tablespoons of lemon juice and season with salt and pepper to taste. Be careful with the lemon; if you add it too soon the milk will curdle. The result of it done correctly will be a shiny smooth sauce.
Meanwhile, bring a large saucepan of lightly salted water to a boil. Add noodles and cook until tender; about 8 minutes. Drain.
Fit a steamer basket into a saucepan and add 5cm of water, 1 tablespoon of butter and remaining 2 teaspoons of lemon juice. Bring to a boil and add broccoli. Cover and allow the broccoli to steam for 5 minutes or until tender but still bright green.
To finish the dish mix together the sauce and noodles then place them on a serving platter. Top with chicken in the centre and arrange broccoli around the outside edge.