The right way to fix school lunches is actually radically simple.
incentivize schools to have kitchens again, where food is made from scratch, instead of subsidizing frozen goyslop from mega manufacturers whose only concern is saving a nickel.
When I was a kid, lunch ladies made the food. Every week, we had soups made on a regular rotation that incorporated leftovers from the previous day's lunch. They baked their own rolls! They had ingredients out for salads. This wasn't some crazy fancy school, it was a dismal rust-belt sort of place, but the lunch ladies cared. Their kids all went to that school district. They were cooking from the heart, and even though their ingredients were humble, they often did a really good job. It wasn't all great, and some days had slop, but to me, the worst days were the ones with that cardboard "pepperoni" pizza rectangle and some sad carrot sticks. I'm sure it gave the lunch ladies a good day of respite to be able to do that instead of making pot roast or chicken a la king or whatever, but it was awful. Somehow, every kid had it in their head that the pizza was the "good" day of lunch, but I couldn't stand it.
Even by the time I was in high school, fast food and ready-made meals were invading and the from-scratch cooking had slowed to a trickle. Lunch ladies were now just heaters of slop, with no pride in their work and often with no children of their own. From what I can see, there's zero cooking at my old school now. It's all just reheated.
Those jobs had more dignity and the children were fed better when the food was made in the schools. It's time to bring that back, even if that means having to initiate a jobs program to re-train people on how to actually make food on a school-wide scale instead of just heating it up, and a grant program to ensure that schools have the equipment and training they need to be successful "onshoring" their food service operations.