Pasta in tomato sauce with hamburger (or without), mini meatballs (chicken, turkey, beef, pork etc) homemade chicken nuggets...I'll keep thinking, I'm sure there is more its just not coming to mind right now. Does he eat pizza yet? My two DD's love pizza so we keep a stock of frozen pizza shells in the freezer and just put on the toppings and toss them into the oven. Its a nice quick lunch. I make our shells so that I can make them different sizes for the different people in the family, but we've used store bought ones cut up before too.
All those can probably be cooked, frozen and reheated, or frozen raw and just thrown into a dish and cooked pretty quickly.
What about things like grilled cheese? Or cheese cubes, lunch meat and fruit chunks? Things that dont have to be frozen, or really cooked and are simple to get onto a plate and into a hungry child.