This 3-4-3 system isn't working at all. Lacazette isn't getting enough support behind him or either side of him. If we were playing 4-2-3-1 he'd at least have the number 10 to play off and thread him through. Too often in this system he looks isolated. The only play I can see working up front in this system is someone like Alexis.
Giroud scored 11 goals in total for his debut season. Even on his best days he's had seasons where he's gone 8 or more games without scoring. I wouldn't put him in this system and expect the problem to be solved.