only suggestion I can make is offering veggies - whether as part of the meal with meat etc, or other ways like with hommus, natural yoghurt, salsa, avacado, as a soup, with bolognaise, etc - lots of different ways, different textures, different temperatures etc.

and only offer fruit/sweet yoghurt/etc *after* mains.

while DS still favours grapes and banana over carrots and pumpkin, he'll eat a lot more veggies when there's no fruit on display