Alongside what others have recommended, I’ve found that running through scientific case examples and trying to get them to come to the conclusion themselves (for example pointing out that a river dips to a certain area or that vegetation in an area is missing) helps to teach critical thinking without a pro or anti-religious bent. It’s also a tad bit of a buzzword today, as it encompasses many skills, but in my opinion (which isn’t the only one) one of the most important base skills is a firm understanding of hypothesis tests.