Best veggies to add to a Mexican soup?

I make this awesome soup with beans, chicken, green chilies, tomatoes and cilantro. It is really spicy and so yummy! I am wanting to add some veggies to it without really changing the flavor. I am not a fan of corn in soups, at all. I am thinking maybe zucchini. What about tomatillos? I have never cooked with them. What kind of flavor do they have? Any ideas welcome! Thank you!