can i tap fiora by attaching shady spectacles onto a 1 might unit copying a 5 might unit

Yes — the 1-Might unit goes from 1 Might to 5 Might while already on the board, which is exactly a "becomes Mighty" transition (Rule 709), so Fiora, Grand Duelist's ability triggers and you may exhaust her to channel 1 rune exhausted.

Shady Spectacles's copy effect changes the equipped unit's Might from 1 to 5 as it attaches, and Rule 709 doesn't care how the change happens — the unit was in play at 1 Might (not Mighty) before the attach, then crossed to 5+. This is the same situation as moving a unit onto Trifarian War Camp triggering Fiora, since the unit is already on the battlefield when it gains Might (FAQ #5835). It's unlike playing a unit that enters already at 5+, which never transitions.

Two caveats: the equipped unit must not already be Mighty before the attach (an already-5+ unit buffed further doesn't trigger, FAQ #9584), and Fiora must be readied — exhausting her is the cost, so a tapped Fiora's trigger fires but can't be paid. Also note the copy only takes the target's printed Might, so if your "5-Might unit" is only 5 from attached gear, the copy comes in lower and won't trigger.