This is a crowd pleaser. I'm making no claims of authenticity. It's the recipe off the back of the chow mein noodle package, with a few tweaks.
I use cooked ham at school so students don't need to worry about cooking the protein through. At home, I'm more likely to use chicken or raw pork, in which case I would add it at the beginning of the cooking process. Carrot is more traditional than bell pepper. I use bell pepper at school as it's easier to practice knife skills with. At home, I'd likely add both. Or neither. Whatever.
If you are using raw chicken or pork and want to be a bit extra: cut up the meat and then place it in a small bowl. Mix together a teaspoon of corn starch with a bit of water. Mix them into a slurry. Toss the meat with the slurry, some salt and pepper and a tablespoon of soy sauce. Let it sit for a few minutes before cooking it. The cornstarch gives the meat a "surface" that will brown better than without it. The salt/pepper/soy season and tenderize the meat.