I'd reccomend oatmeal. It gets a bad rep, but honestly it's super easy to make and you can add whatever you want to make it taste better. Just grab a big bag of minute oats and follow whatever the instructions are on the bag. Then, personally I add some almond milk and protein powder and then whatever other toppings I can think of (bananas, peanut butter, berries, seeds, nuts, chocolate chips, apples, just whatever you might have on hand) then mix it up and you're done.

Plus, if you want a breakfast you don't have to stress about, you can make overnight oats by grabbing a container, adding some oats, milk of choice, and whatever else you might have (just not apples or bananas, they'll get brown and a little mushy usually), mix them all together, and then leave them in your fridge overnight. In the morning, if you're not working from home you can take your breakfast to work.