BUBBLE BOBBLE Neo!

Rather than hunting down letter bubbles, I found a much easier method of making the giant foods appear. Start up a game of Arranged Mode. Whenever you see a teardrop-shaped gem appear, grab it, because once you've wiped out all of the enemies, a giant fruit will drop. I've found the teardrops to be very common in the first 10 lvls or so of Arranged Mode, so my strategy was to restart from lvl 1 after noticing the drops became less and less common. The 20 are cumulative and do NOT need to be grabbed in one playthrough.

This probably won't be seen by many people at this point, but if it helps one or two people get this achievement quicker, it was worth posting. :D

The way to make a big food item appear is to grab a 'Magic Cane' item. When you collect one of these, all remaining bubbles at the end of the stage will turn into small food items and a big food item will appear in the middle (the small food items will be the small version of the big food item). To make a Magic Cane item appear, you have to collect 3 of a certain 'EXTEND' bubble. For example, if you collected 3 'T' bubbles, an Orange Magic Cane would appear as the item on the next level. The counter carries on over levels so you do not need to collect the same letter three times in one level, but you do need to collect them all in one game. Just collect 20 magic Canes, finish the levels you got that item on (to make the big food item appear) and the echievement will unlock as soon as you scoff the 20th big food.