Masters Degree

As I've mentioned before, I'm currently in a post-bacc teacher credentialing program. I am getting a credential to teach high school math. Well, high school or middle school math. I'm not sure which I'll do yet. But I digress.
I am already thinking about what kind of masters degree I'd like to get upon the completion of my teaching credential. I've always been a bit of an over-planner. This time, planning far in advance will be helpful, though. Since I'm already going to school, it's relatively easy for me to complete any pre-reqs for a masters program. Plus I'm already on-campus to speak to advisers.
I thought about doing a masters in math with an emphasis on math education. The problem with that is that my college degree required exactly one math course. That means I'd have major work to do to complete the 24 units of pre-reqs, especially considering the sequential nature of math classes. Specifically, it'd be like 4 semesters of Calculus. That can't be rushed. Speaking it over with my husband, we decided a math masters is not for me. To be honest, the reason I'm going to teach math is that there's a huge shortage in the subject and therefore there are a lot of jobs. I've always liked math, but it's not my passion.
Maybe something like Environmental Science or something to do with animals would work. Those are both things about which I am quite passionate. Any recommendations?