how to refer to mobs spawned with (spawn entity)

im working on a mod for me and a friend and one of the things that it adds is a command "/zombieapocalypsestart" i want the command to spawn alot of zombies and have all of them target the player who did the command no matter how far they spawned, and i thought i could do this with the "set attack target of _____ to ______" block however i dont know how to specify that i want the zombies that i spawned to target the person who did the command can anyone help?