You must build your own base and progress through various waves. You can build/upgrade what you want, but nothing respawns if you lose them. Building more Cities gives you a faster cash flow, but then you have less defenses. The only way to be successful is to have a good amount of bases and upgraded Light Guns. Keep everything close together to be shielded. This will take many successful wave defenses to gain enough "extra money" to get the lasers. You must build 4 Laser Towers which costs a total of 1200. After building them you just have to fire on the screen so that they all shoot at once. Below is the suggested method to gain the achievement easily.
Modifications needed: Battle Cry and Lazy Mode
Stage 1: 1 Light Gun and 1 Laser Tower put next to the City.
Stage 2: 1 Light Gun and 1 Laser Tower (opposite sides of stage 1)
Stage 3: Do nothing
Stage 4: Build last 2 Laser Towers.
Now after all your lasers shoot, let yourself die and gain the achievement.
Thanks to Mieces87 for Lazy mod tip