I use a mouse button bound to Alt-T to fire torpedoes. I've used it this way since I started playing over 800 days ago.
Now, with Season 6, and issue I reported while it was on Tribble has strangely been pushed live - the letter T seems to be hard-coded to open Transwarp Destinations unless it's specifically bound to something else.
If you look in the space key bind section, you'll see that there is nothing by default bound to Transwarp destinations. To keep the letter T from opening the Transwarp menu, you have to bind it to something else... I worked around the issue by binding T to fire torpedoes, but I didn't have to do this before S6.