This achievement is cumulative across all games and modes. You will most likely not have completed this after getting all gold medals. I only had around 250 after getting all golds, but I barely ever used any of the delayed power-ups except the magnet.
To boost this, I would recommend Military Level 6. This levels objective is to introduce you to the nuke, and requires you blow up 30 objects just to complete the bronze requirement. You can easily earn 40 to 60 objects destroyed per attempt of the level. Make sure to use up all your lives and you should have this achievement in less than 30 minutes.