Despite how specific and odd it sounds, Master Blaster is actually particularly easy, as the Rocket Zombie's natural weakness is Snow Pea and because Snow Pea is unlocked after reclaiming The Post Office Lot, the lot that must be reclaimed before getting to Killjoy Park, the world where the player first meets the Rocket Zombie. You will most likely get this achievement, as you use the new plant unlocked, which was Snow Pea, to take out a Rocket Zombie on the first level. Along with that, one of the loading screen tips said "Snow Pea takes out Rocket Zombie's rocket!"