Boil the orzo according to the instructions on the box.
In the meantime, heat up the butter in the frying pan.
Peel and cut the onion in small piece, add in the frying pan.
Peel and press the garlic in the frying pan.
Cut the mushrooms in small pieces and add in the frying pan.
Add the salt and pepper and mix.
When the orzo is ready pour away the water and add the orzo to the frying pan and mix well.