Loft the Boomerang bird over the main structure, spinning it back into the triangular support in the bottom-right corner. Make sure the falling debris pops the the rightmost pig. Fire a Yellow bird straight ahead, through the two vertical wooden planks. This should clear all pigs, but use another Yellow bird if there’s any need.
Go straight into the left of the main structure with the Boomerang Bird to the square hollow wooden block. Then, wait for everything completely fallen, use the Yellow Bird to break the brown cake under the main structure and the whole left and middle of the structure will be destroyed. Most of the time, the right part of the structure still stand there so use the third Yellow Bird to make it fall onto Helmet Pig's head.