I always have steamed rice with raw egg and soy sauce, it has everything I need after a run, carbs, protein and a bit of salt. It's also surprisingly delicious! Sometimes i have a bit of tofu in there as well, and some vegetables when I can be bothered to actually cook.

Tamago Gohan to Start the Day, Breakfast: Food + Cooking : gourmet.com

It's easy and simple to make, tastes good, and definitely a great start to the day, I strongly recommend it.

Porridge is good too.