IMO, this achievement is not really hard, I did it at the 1st try after viewing the guide.
Just set to 5 lives, play at stage 1, eat most small pellets on the screen, you may die when doing that.
Then just run around and let the ghosts tail you. Once all 4 ghosts group together, move to one of the corner, stay. When they are very close to you, eat them all at once!