“natural” and “flying spaghetti” are themselves creation. I am not convinced that something we could observe/imagine would be the original Creator of everything, including this (observable) universe, living organisms, biological systems, consciousness, aesthetic nature of this world that couldn’t have formed solely by survival method of evolution, etc. It has to be something outside of this Universe to have the capability to create this Universe.
The truth is, we are giving a very limited knowledge and scope to which we see / can imagine things. God created all this as a test for us. It’s like a simulation where we are the characters. Certainly we have been given the task, what we need to know, what to do and what not to do. When this test is over, we’ll surely see the ultimate reality, and the results on how we performed in this temporal test.
Back to your question, how do we know it’s God? (Allah?) .. it’s because if someone did create us, it’s surely for a reason. And definitely we must be given some instructions. We just need to find those instructions. Look around you, there aren’t many religions. It’s a known fact that only one religion that has the instructions preserved and free from contradiction. Only ONE! (i.e. Quran). Surely the One who wanted us to follow instructions, pass a test, would have preserved those instructions.
Quran is how we know for sure, that it is not a flying spaghetti monster, nor a natural cause (because natural cause would require nature to exist). It is indeed He, who has sent this Book. It is surely One God, and certainly we will be returned to Him.
اَمْ خُلِقُوْا مِنْ غَيْرِ شَيْءٍ اَمْ هُمُ الْخٰلِقُوْنَ
“Or were they created by nothing, or were they the creators [of themselves]?”
(Quran – 52:35)