I have a couple of standby breakfasts that work well for me. I tend to get in a routine and eat one version for a week or more, then switch to something else.
My standbys are:
Fage greek yogurt w/ frozen blueberries
Steel cut oats with shredded sharp cheddar & V8
PB on a piece of whole grain bread (basically 1/2 a pb sandwich) and a sliced apple
Blue Goodness smoothie (whole bottle, which is 2 servings - this is rare, in the nature of a splurge for me, because there's not much protein in it, and I'm all about the protein!)
I rotate through these options regularly.

Each of them is 340-ish calories, give or take. I think the lowest is the yogurt and blueberries, at under 300 and the highest is the pb sandwich and apple at 350.
But they all keep me full until lunch and they all give me a good boost of protein or fiber.
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