Preheat oven to 350 degrees F. Over medium-high heat, sauté onion and bell peppers in canola oil and chicken broth for about five minutes. Add zucchini and sautè for about three minutes or until just cooked. Remove from heat and pour off any excess liquid.
In a large bowl, combine chicken and vegetable mixture. Add cilantro, green chili peppers and garlic powder. Mix thoroughly. Stir in 1 cup of grated cheese.
Layer about 1/2 cup of enchilada sauce on the bottom of an 11x17-inch shallow baking dish coated with nonstick cooking spray. Pour remaining enchilada sauce into a large bowl.
Dip a tortilla into the bowl of enchilada sauce until it's completely coated on one side. Then fill with two large spoonfuls of the chicken-vegetable-cheese mixture. Roll tortilla into a tube and place in baking dish, seam side down. Continue dipping and filling tortillas, and place each tortilla in baking dish so they touch.
Top enchiladas with remaining sauce and cheese. Cover baking dish loosely with foil and bake 12-15 minutes. Remove foil and bake 10 minutes more. To serve, garnish with olives and light sour cream if desired.