Add anything with some fat to the turkey to make it less lean?
I find anything leaner than 80/20 beef is near impossible to keep juicy. Imagine ground turkey or chicken is really difficult. And those aren't meats you can safely cook medium or less, so even more tricky.
Not this time, but that's something I'll have to keep in mind for next time, I'm always trying to experiment and try different stuff while grilling. They weren't as juicy as a typical beef burger, but the jalapenos helped make up for that.