Oatmeal. Pour in bowl with water/milk and nuke it for 3-4 min. Or you can do the whole overnight oats thing and have it ready with no prep in the morning.
I second oatmeal but I go with savory. 50g of oats, 250ml of broth/liquid.
Variation 1 is a spice mix that mimics a favorite rice pilaf recipe (maybe 1/2 tsp of Old Bay seasoning, some salt and pepper, a sprinkle of turmeric and coriander). Then add in protein, veg, cheese, whatever. That's my go-to most of the time.
Variation 2 is "pizza" style: a scoop of premade marinara, some broth to fill out the rest of the liquid, and a sprinkle of shredded mozz. Throw in some protein/veg that works (think pizza).
Variation 3 is "Mexican style," which I mostly do if I have some leftover carnitas or taco meat: change the spices to chili powder and cumin, cheese, of course.
Quick oats cook up in 2-2.5 minutes in the microwave. Total prep time is maybe 10-15 minutes.
Oh damn I never knew you could do oats like this. My wife recently went on an oatmeal kick and did overnight oats with peanut butter and milk but I had a real hard time with the texture/consistency of it.
It took me a moment to get used to it, because I had the traditional upbringing with oatmeal = cinnamon, sugar, etc. But it's not that different from mashed potatoes, polenta, or rice. I already had the pilaf recipe that was a favorite "go with anything" side dish, so I tried that first and stuck with it.