How do I make my lizards grow faster and get fatter? and whats the best thing to eat?

I have 3 Iguanas, 3-4 yrs old, a juvenile 2yr old, a 1 yr old and I have one Chinese water dragon who is about 2-3 years old, What should I feed them to get them fatter and They aren't really growing a lot, What should I do about it? and give me the best names for repti vitamins