I don't actually plan on using the word "evolution," which is why I haven't found a good way to ask the question.  Basically, my idea is to show the students different animals, and different features they might have.  For example, camouflage to hide, fur/blubber for warmth, different types of teeth for different types of food, eyes of predators vs. eyes of prey, and things like that.  Eventually, I want to allow the students to randomly choose conditions such as the animal's environment, food, size, if it is nocturnal, etc.  Then they will design an animal that would be successful in those conditions, and discuss how/why they made those decisions.

I think you should teach evolution, however I would tread lightly.  I also have a religious co-teacher.  To give you an idea of what you might expect, I recently had a picture of a monkey making a funny face on one of my power points.  She stopped my class so that she could chastise me for "reminding her of evolution" and how the world was actually created in seven days by God, etc. I didn't even mention the word "evolution".  I was teaching emotions and it was just a monkey and now I'm no longer allowed to use monkeys in my presentations.  So god speed and good luck!