1 part oatmeal (1 dl for a small meal, 2 for a bigger one)
1.25 parts water
Some salt
Optionally some psyllium seeds for extra fiber, maybe a teaspoon
Extras
Some milk, maybe 1 dl
Some lingonberry jam, maybe a tablespoon
Mix everything in a bowl
Microwave for 2 minutes for 1 dl oatmeal or 2.45 for 2 dl oatmeal
Mix with a spoon
Top with jam and pour over some milk (careful, it's hot)
Ready to eat in five minutes, very low effort, produces little in the way of dishes to clean, cheap as dirt, vegetarian if using cow milk and vegan if using oat milk, and not particularly high in calories but still quite satiating. Downside is that it's not the most exciting meal you could think of, but you arguably get more than you pay for all in all.