You achieve total destruction in Year of the Dragon level 1-7 is pretty straight forward. Use the yellow birds to destroy as much of the structure as you possibly can. Fling the fish so it lands on the ground right in front of where the structure used to be. Good luck!
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I threw the koi to the gap near the boulder.
Launched the fish to hit the flower and come to rest next to the left stone block with the red/black inside.