Buddhism is a fantastic system that is internally consistent and to our ability to prove it, accurate. Its primary axiom is that life as we know it is suffering, and builds a case for a universe from there that is primarily mental. It is from these observations, not pleas of faith, that the metaphysic is built up rather rationally. It behaves more like a science in many respects, with religious trappings that confuse the westerner. For example, one of the main tenets being skepticism: if you cannot prove what the Buddha stated then reject the model.
Non-duality is absence of an observer in observing, taster in tasting, toucher in touching etc. There's only observing, tasting, touching etc as a process starting with a contact (the coming together of a sense organ with its object) , sensation , perception or recognition , mental or karmic formation (viewed both as a verb and as a noun) , and consciousness of the mental object.