Dice the onion and sweat in a pan with oil.
Meanwhile, microwave the peas according to the instructions on the back of the pack and then add them to the onions.
Once the peas and onions are cooked, use a stick blender to mix them together in the pan.
Chop the mushrooms and add them into the pan with the remaining ingredients.
Simmer for 5 minutes and add seasoning to taste.