Almost any meal raises your natural insulin levels. Pure protein raises it the least, while combinations of fat and simple carbs elevates it the most. There is an article on the insulin index of foods located
here -- insulin index is a little bit different from the glycemic index, which you've probably heard of. The latter measures how much your blood sugar rises in response to certain foods, the former measures how high your insulin levels spike in response to the blood sugar response to foods.
Basically, you're going to try to spike your insulin when your muscles need fuel (after and maybe before a workout, and first thing in the morning) and keep it low the rest of the time, when insulin would probably shuttle nutrients to fat cells, rather than muscle cells. There's more info in articles all over the place, such as
here.
Incidentally, this whole insulin thing is the reason why fruit sometimes gets a bad rap in bodybuilding. Fructose (from fruit and high-fructose corn syrup) is metabolized into glycogen in the liver, for later release during times of low blood sugar. Muscles cells, however, cannot use fructose to replenish their own glycogen stores. So if your liver is full of glycogen, the extra fructose gets sent off to form triglycerides or metabolized into fat, rather than going to your muscles. Still, if you just eat fruit when your liver glycogen stores are low, such as in the morning, this'll never be a problem.