When we were broke, eggs were always a good standby. We didn't use a microwave, but I have had microwaved eggs and they're decent enough. https://www.foodnetwork.com/how-to/packages/food-network-essentials/how-to-cook-an-egg-in-the-microwave

You can have mug cake for dessert: https://www.allrecipes.com/recipe/241038/microwave-chocolate-mug-cake/

Microwave potatoes, veggies and ham with a little butter. If you add warm milk afterwards, it's a soup.

Tortillas with cheese and whatever other topping. They get kind of weird crispy, but it's better than a lunchable.