Develop a musical piece using the given theme and incorporating the letter-based structure provided.
X:1
L:1/8
M:4/4
K:Dphr
['F2 G2', 'z DED']  
X:1
L:1/8
M:4/4
K:Dphr
"A" |:"D" F2 G2 A2 FD | GF- F6 | F2 G2 AGBA |"Gm" G4- GGAB |"Cm" cA B/A/G AF G/F/E | 
"D" GF- F2 z DED |"D" AGAG"Cm" FDEC |"D" D2 F2 A2 d2 |"Cm" cA B/A/G AF G/F/E |"D" GF- F2 z DED | 
"D" AGAG"Cm" FDEC |"D" D8 :|"B" |:"Gm" G4 G4 | G2 G2 G2 D2 |"Gm" DBAG"D" ^FGAF |"Gm" G4 z DED | 
"D" F4- FDED | A8 | ABAG FGAF |"Gm" G8 :|"C" |:"D" DF/F/ FF F2 A2 |"Cm" GFED C4 | CEDC FGFE |1 
"D" D2 G2"Cm" FEDC :|2"D" D8 |]  