I made this last night and it was delicious this morning and REALLY filling. http://minimalistbaker.com/peanut-butter-overnight-oats/

Looks like not enough food when you're mixing it up the night before, but I shared it with my toddler and it was more than enough, esp with some fruit.

I didn't have unsweetened almond milk, so I just used original flavor and left out most of the maple syrup.

Op here. Wow, thanks everyone!! Tons of good ideas here that would never have occurred to me. I'm going to try a couple of these and report back. I'm hoping once he tries something healthier and then realizes he isn't starving and hangry a few hours later that he'll want to switch of his own free will

On the weekend make a big batch of breakfast burritos and freeze them. Reheat in microwave for 2-3 minutes. We do this during ski season and it's great.

agree with all eggs ideas, my 10 yo can do scrambled/sunny side up/easy over etc, and nuke bacon in the microwave. Add English muffin to toaster - breakfast sandwich is ready.
I understand however that teenagers won't do it every morning, weekends only when they don't have school bus @ 7 am
Quick favorites for my older DS were plain Greek yogurt or cottage cheese topped with maple syrup/honey/craisins/raisins/walnuts. Sometimes he'll go for smoothie (frozen berries/banana/milk/honey).

To replace the sugary cereal maybe include a fruit smoothie? Strawberry and banana, splash of coconut or almond milk and handful of ice cubes. This in addition to some of the ideas posted.... I have an athletic 17yo son who thinks PopTarts are an acceptable breakfast and then he is starving 2 hours later. LOL