Another work of art, made by me on paint… but its easy to follow. Since you can choose which level you want, go to level 5 and follow these steps while referring to the picture:
(The purple square is your player, the red and green squares are the enemies, and the brown squares are the rocks in the level.)

• Start off following the purple arrow going left and up. Immediately after the red enemy turns away from you, go up (but do not break ALL the way through the dirt) then go back down and follow the blue arrow.
  
• Wait above the enemy cavern until the green enemy turns away and dig right through, following the aqua arrow to the bottom of the level.
  
• Once at the bottom, go right and up, straight for the rock near the top of the level. Before you get to the rock you should have 4-5 enemies behind you, or close to being behind you.
  
• Once you hit the rock, go left or right at the top (red arrows). Sit back and watch your 4-5 enemies get squashed.

You must dig EVERY BIT of dirt on the screen. Your screen should be completely black. This is probably by far the hardest achievement in the game, but its doable. Start in level 1 and kill 2 enemies. DO NOT kill the third enemy or the last one will leave, and you will advance to the next level. Now go back and forth, or up and down, avoiding the last 2 enemies as much as possible until you have no area to clear in the paths you made. Now go back and forth or up and down (depending on how you did it first) to clear the rest of the small debris on the screen… you have 3 lives, stay alive as much as possible and good luck.

Edit: Supposidly this achievement is glitched for a lot of people, but its not unobtainable... i got a suggestion from someone over at xbox.com on how to help and it seems to be working for most people now...
if anyones having trouble, just do your normal thing and clear the stage until theres no more dirt... Go around the outside of the screen clockwise, then counterclockwise and get killed in that same level afterwards.

The pineapple can be obtained in level 18 and beyond for a few more levels, after dropping two rocks in the same life. Try killing off all but 2 enemies to make it easier on yourself.

EDIT: For all of the fruit/vegetable gathering achievements, you do not have to drop 2 rocks in the same life MOST OF THE TIME, just 2 rocks total.