What is a nutritious, filling, and easy to eat breakfast for really early in the morning?

Steel-cut oatmeal is super-easy, set-and-forget (1 cup water, 1/4 steel-cut oats, pinch of salt, Bring water to boil, stir in oats, salt, lower to bare simmer, uncovered 30 minutes, flavor as desired, eat).

But that can get boring. For something a little more exciting, super-nutritious, and almost zero-prep, do a sort of Norwegian-style open-face cracker (no, you don't need "the tubes", but if you can find them, knock yourself out). For this I take a tin of fish (usually smoked salmon or trout, but sardines, mackerel, or even tuna would work fine), a piece of cracking toast or a Scandy flatbread cracker (Wasa, knekkebrod), and some kind of "schmear" (a thin spread of cream cheese, sour cream, yogurt, or - my favorite - Trader Joe's Everything But the Bagel Yogurt Dip/Spread). I can get all these ingredients both cheaply and well-made at Trader Joe's (TJ Smoked Salmon in a tin, TJ Norwegian seeded flatbread, and the aforementioned dip). For a little additional oomph toss on tomato or cucumber slices.