In a saucepan, melt half the butter over medium heat.
Add onion and saute until soft. Season with salt & pepper.
Stir in barley and cook for 1 minute...then add your broth and water bringing to a boil. Cover, reduce heat and simmer just until barley is tender and liquid is absorbed (about 30 minutes). Remove from heat but keep warm.
Meanwhile back at the ranch melt the rest of your butter in a fry pan. Add your mushrooms...cooking over med-high heat until they have no more liquid. Add in your lemon juice and parsley. Mix to combine.
Scoop your barley into a serving dish. Drop in your mushrooms, give a little stir, a little more fresh parsley and you are ready to eat.
Notes
Choose Pearl barley if you can as it requires less cooking time. Pot barley can take up to an hour to absorb all the liquid and be cooked through.