Saute the onions, chicken and garlic in a non-stick pan. If you don't cook it too hot, cover it and add a bit of water if it starts to stick, you can do it without any oil at all. Add the zucchini, corn, chiles, canned tomatoes and seasonings and cook another 5-10 minutes. In a bowl, mix the dry ingredients well. Add the wet ingredients and the chiles and corn and mix until just blended. Pour the filling into a casserole sprayed lightly with nostick spray and top with the corn mixture. Sprinkle the cheese on top and bake, uncovered at 180ºC or about 20 minutes until it's quite bubbly.
Less than 10 grams of fat per serving and if you used non-fat cheese it would be considerably less.