Preheat the oven to 375f.
Heat the oil in a 2 quart stove-top covered casserole. Add the garlic and onion and saute over moderately low heat until onion is translucent (about 5 minutes). Add the mushrooms and saute over moderate heat until mushrooms are golden (about 5 minutes).
Add the barley and basil to the mushroom mixture, and toss lightly.
Poor in the vegetable stock and season with salt and pepper. Slowly bring the casserole to a boil, then remove it from the heat.
Cover and bake in the oven until the barley is tender (45-50 minutes).
Before serving, add the chopped parsley and toss gently. Serve piping hot.