Ooh I’m finding lunches hard as well, because toast is such an easy breakfast in the morning and the only one Dd will reliably eat. She’s the same age as your ds.
I’ve had success with tortilla pizzas - a wrap spread with tomato purée/passata and then finely diced veg sprinkled on top with a bit of cheese, in a hot oven for 5-7 mins.
Tuna fishcakes - can tuna, breadcrumbs, grated courgette and an egg mixed up and then fried. She has hers with salady bits and quite likes them
Eggy muffins - i chop up spinach, tomatoes and courgette into small pieces and then mix with a couple of eggs and some cheese and then pour this into muffin tins and bake for 10 mins until set. These freeze really well and can be microwaved so make a super quick lunch.
Homemade soup with crackers, she’s obsessed with dipping at the minute, so any smooth soup she loves. Bloody messy though!
I roast a batch of chicken legs at some point in the week for sandwiches/pies/curries etc so she’ll often have cold roast chicken with chopped veg, hummus and a yogurt.
Pasta salad, I make too much pasta if we’re having some in the week as it keeps ok in the fridge for a couple of days, so mix it with veggies and creme fraiche to make it creamy but not salty. That one goes down especially well.
Hope that helps, will be keeping an eye out for more ideas!