Let's say a Scizor uses Bullet Punch, which is 40 BP, then that 40 BP is boosted to 60 BP. Under the effect of Technician, that 60 BP should also be boosted to 90 BP. Does Technician actually boost Bullet Punch once or twice?
In this case, since Scizor gets STAB from Bullet Puch, it would get the boost from Technician to 60, then STAB to be 90 base power. Bullet Punch would get only 1 boost to 60 base power, not twice to get to 90 base power if there was no STAB. It would be the same if there was STAB because Technician only gives one boost, not 2.