My 14 mth old is milk, egg. peanut and soy free due to severe allergies. Shes not big on veges, but eats a lot of fruit.
Citrus fruit or kiwifruit increases iron absorption so if bubs won't eat a lot of meat, giving them citrus or kiwi for dessert maximises the iron in whatever meat you manage to get into them. If bubs won't eat veges but will eat fruit, they will generally get enough nutrients from the fruit.
I add finely diced spinach to plain rice. I bring the rice to the boil, then add the spinach and let it simmer until the rice is cooked. Maya won't eat spinach on it's own, but eats it like this.
Also, i make a mince stew - mince, potato, kumara, carrot and brocoli boiled slowly together in beef stock, then mashed. She likes to eat this herself with a spoon (and some help!).
Broccoli is a great vege for toddlers, it looks appealing, and has a fairly bland taste if boiled.
Root veges are great coz they are a bit sweet, so quite palatable for young kids. I mash a bit of boiled liver into kumara and pumpkin, liver is great for iron, and the veges mask the taste.
Also, frozen peas or mixed veges that they can pick up themselves with their fingers. Like Kristi said, a lot of the time they will feed themselves what they wouldn't touch if you were feeding it to them. Also, if you eat at the same time, it is encouraging for bubs. Maya and I have dinner together most nights, so she sees me eating the same things as shes eating.
Maya is underweight for her age and I used to panic about everything she ate, but now i just aproach mealtimes by thinking, I'll offer what I offer (meat and veg, fruit and bread) and if she's hungry enough she'll eat.
Good luck, let me know hoe you get on!
Mum to Maya Grace 02-03, Sienna & Mercedes 10-06