Pretty broad recipe, this one.
You will need:
Oatmeal
Stock or broth of your choosing (chicken, beef, vegetable, etc)
Vegetables of your choosing (mushrooms are hardly optional though)
Spices of your choosing. Usually I just use pepper, salt if the stock wasn't already fairly salty, and garlic or onion powder if I didn't put fresh leek or chives or something in there.
Cheese of your choosing (again, optional but not really)
Step 1: bring stock to a boil
Step 2: add oatmeal and vegetables
Step 3: simmer until it's all cooked. It will need stirred a lot.
Step 4: add cheese
Step 5: done