DS1 is 5, and declared last night, that despite him liking separately, meat, pasta and cheese, the lasagne smelt like poo. I use with him the old "I expect you to eat 5 mouthfuls of that" It generally works as he likes counting down to none.
Both my DS also seem to like all their veg raw. He ate a courgette while I was cooking, then after it was cooked, refused to eat it. I just go with it now. My DS2 2yo, will eat more if we feed him. I tend to put a selection of raw veg on the side, carrots, courgette, broccolli, cauli, with some hummus, which he loves, and he will dip them in. I find if I'm sitting with him, and do something with my food, then he will also eat more, as he's wanting to try what I am doing.
I've found there is no magic answer. I don't use the no pudding unless your meal is eaten thing either. Growing up my mother and us had magnificent battles in the food area, but there are just some things I didn't and don't like . I don't want to go down that road.
I do like the suggestion of the food taster chart, this would be great for them to see all the different foods they've tried. I've tried meal planning with DS1 but he's not into it, everything he see's he says NO to. For lunches I've resorted to lots of snacking things, packet of biscuits, fruit pouch, actual fruit, cheese and this week the big hit has been small pepperoni sausages with some mini pita's for filling him up. Give them whatever works, small bits, and a good variety, that's been a saviour for this weeks' lunches.