Madagascar Kartz

Melman is unlocked from the beginning of the game (he is the giraffe). Simply pick quick race or championship and play as him. I recommend Championship since you can also knock out a different achievement at the same time. Playing on 50 CC is obviously the easiest to win with.
If you're having trouble winning you're probably not taking advantage of the power-slide feature along with turbo. Make sure to slide around each corner to help fill up that bar.