Once upon a time, when the Buddha was caught in the life cycle of birth and death and in one birth, he was born as a rabbit.
Every full moon day, the rabbit always observed the precepts in order to devote his life to the holy metaphysics with the intention to preserve and deeply concentrate on the dharma leading to the Buddha hood.
One full moon day, the Indra knew about this and he disguised himself as an old Brahman and begged for his flesh as food. The rabbit agreed to devote his life for the old Brahman. But he old Brahman said "I have practiced the precepts for a long time and I have never killed any animal".
Then the rabbit told the old Brahman to light fire in order for him to leap into the flames to death. But before jumping into the fire, he wished:"May my head locate in the center of the moon".
After that, the rabbit jumped into the fire, so that the old Brahman could have his flash as his food as he wished.
Under the power of the Buddha, the shape of the rabbit has appeared in the center of the moon as we see nowadays.
Afterward, in order to dedicate to the the birth of the rabbit, we celebrate the "Auk Ambok Sampeah Preah Khe ceremony". This ceremony is salute the head of the rabbit. The people choose the food that is suitable for the rabbit such as bananas, pounded rice, potatoes, coconuts and taro for traditional dedications ever since.
Thus the people celebrate the Auk Ambok and Sampeah Preah Khe ceremony on full moon day of November because it is the end of rainy season and it is the time that is rich in bananas, pounded rice, sugarcane, taro and potatoes etc...