My kids (3.5 years old) will go back and forth on vegetables. Some days they will eat them without issue and other days, they just refuse the ones they were willing to eat the other day. When I get really concerned that they just aren't getting enough good stuff in them, I resort to those baby food self-feeding pouches. There is something about them being able to eat directly from the pouch that makes them want to eat it. I won't pretend to understand. It seems like a room temperature pouch of Spinach, Pears, and Peas cannot be more tasty than the non-pureed version. But, at least I know they got something good in them.
I've been trying to reduce the dependency on the pouches, but sometimes getting them to eat some vegetables is better than nothing.
Sometimes giving my kids a choice beforehand helps. Do you want broccoli or zucchini? Sometimes it works...other times they might say "I want goldfish."
For some kids, having them help make it motivates them more to eat it. It kind of works with one of mine, but the other one gets bored with the cooking part that comes after the prep part and loses interest by the time the food is really ready.
I've heard of someone doing color themed meals. I'm not knowledgeable about a lot of diverse foods, but here is one web page with ideas:
http://www.wikihow.com/Make-a-Meal-of-One-Color
I'm just not sure how to fit in a meat portion for the color of the day.