Complex sentence: Puccini had long considered writing a set of one-act operas which would be performed together in a single evening, but faced with a lack of suitable subjects and opposition from his publisher, he repeatedly put the project aside.
Split into simpler sentences: Puccini had long considered a set of one-act operas, to be performed in a single evening. Faced with a lack of suitable subjects and opposition from his publisher, he repeatedly put the project aside.