Compose a piece of music that follows both the given musical theme and the letter-based structure provided.
X:1
L:1/8
M:3/4
K:Eb
['GGA B2 BecA B2 z GGA']  
X:1
L:1/8
M:3/4
K:Eb
 GGA | B2 BecA | B2 z GGA | B2 BecA | B2 z GGA | BAF>FE/D/E/F/ | E3 GGA | BAF>FBB | G2 z |]  