A 28-year-old Indian male presents to the emergency department with acute haemolytic anaemia following ingestion of fava beans at a wedding feast. Laboratory investigations reveal haemoglobin 7.2 g/dL, reticulocyte count 8%, elevated indirect bilirubin, and reduced haptoglobin. Peripheral blood smear shows bite cells and Heinz bodies. Enzyme assay confirms glucose-6-phosphate dehydrogenase (G6PD) deficiency. Which of the following best explains the acute haemolysis in this patient?