I wired a bathroom with a gfci, vanity light, shower light/fan and recessed lights. All have separate swithes and all pull power from the gfci. When I put the recessed lights on a dimmer it trips the gfci and if I reset the gfci it trips the breaker. ( gfci is actually for outdoor use and cannot be reset if protection is compromised or wired incorrectly). If I use a single-pole switch instead of a dimmer everything works fine and is protected. I only have a problem when using the dimmer. Any ideas on dimmer issue?

It depends on how the wiring was set up. Since it trips the GFCI and not a switch, you may have a shared neutral. Not always a good idea to run the lights through the load side since you have no lighting when the GFCI trips. Pull a hot and neutral pigtail off the line side, you should have room, and run the dimmer off that, not the load side. You only need the outlet protected and any light over a shower.