What is an essay topic "GOD IS ONE; PATHS ARE DIFFERENT" ?
You might want to ask your instructor if you could argue against the "God is one" part of the topic. There are religions that would not agree with that statement. You could use your essay to discuss Hinduism with its multitude of gods and goddesses that are different manifestations of the divine, among other polytheistic faiths.
Alternatively, you could focus your essay on the "paths are different" part of your quote. Take your pick of religious faiths from around the world and compare the beliefs regarding God and how to achieve a close relationship with God in each of those faiths. The three most recognizable faiths built on the belief that "God is one" are Judaism, Christianity, and Islam - you will find many commonalities among the three, but there will be differences.
There are different aspects to the idea of "the path" for this topic, as you compare and contrast the paths to God. Considering these as separate aspects might help you to organize your essay better. What are various religions' beliefs about God? What are their rituals? What is their image of God? What are the organizational structures that provide the path towards God? Is there a hierarchy? Is there a belief that one must rely on an intermediary to reach God or that one can reach God without an intermediary? Even the building in which people in different religions worship, their varieties in architecture and decorations, can be part of a discussion about the different paths.