If you want to cook chicken or fish, here's how to do so: Add sliced chicken breast (3/4" thick) or fish (1" thick) on the top of the carrots and onions.
It helps to toss the steamer basket up and down with the cooked vegetables to drain out excess water. This will keep the flavor from being diluted. Make sure you don't overcook the zucchini, as it also will dilute the flavor if overcooked. It will start to look a little translucent when it overcooks.