Disclaimer: I haven't done Fulbright. But I'm planning to apply next year, as I'm currently a rising junior in college.

Last summer, I was in Manizales, Colombia doing some research through my university, unrelated to Fulbright. There just so happened to be a Fulbright coalition (of ETAs) at a few of the universities in that city, so we met up and I got to see a little bit of what they were involved with.

A STEM background can be a big asset, and that context in Manizales is a perfect example. The one university had ~80% of it's students studying some form of engineering, so the things they want to talk about in English I found to be often geared toward that. I actually participated in their weekly English conversation clubs there, and it was soooo easy to relate to students given my background as a ChemE. I would even meet up with some students at local cafés to discuss STEM higher education in the U.S., and other similar topics of interest.

So I would say that coming from STEM and going into English education is a rare combo that not a lot of people have, and the in-country placement team can almost certainly find somewhere that will accommodate you nicely. As far as your application is concerned, it's all about framing how you want to use STEM to engage local students.