Use only a little water as the cabbage will release moisture. Microwave on high for 1 minute and 30 seconds.
Put the oatmeal in a bowl.
Drain the oil from the canned tuna and place the tuna on top of the oatmeal.
Add a suitable amount of mayonnaise.
Mix well.
Heat in the microwave for 1 to 2 minutes.
Season with salt and pepper to taste.