A layer of cells over an area of light sensitive cells offers absolutely no advantage in seeing light better until it evolves translucentness,
The lens of the eye is a bubble of fluid held between two thin, clear membranes.
But a simple pinhole surrounded by a muscular iris does very well, too. (Surely the construction of a simple pinhole camera is something you're familiar with.)
Unless there is some specific evidence to show how this happens, perhaps you all might understand my viewpoint better when I say it takes a little imagination to get it to work.
The natural world provides us with the evidence - for every step on the path to human-like eyes, there's an organism that uses that step for eyes even now. All you have to do is look at the animal kingdom to see the steps of eye evolution.
What doesn't make perfect sense to me (and correct me if I'm wrong) is how the system of metamorphosis evolves by small steps because I can't imagine any possible way that it could happen by small steps.
Why? It's simply the recycling of cellular machinery employed by every organism on the path from gamete to adult. There's nothing that happens in an insect's metamorphosis that doesn't happen to literally every living thing, at one part of its life.
again it seems to me that HOW is left up to the imagination and scientists simply assume that it happened by natural selection because, well, how else is it going to happen?
I wouldn't say the "how" is left up to the imagination; rather, it's left up to the hundreds of thousands of biologists laboring in their field in laboratories and universities all over the world. What did you think biologists did all day? Go over stuff they already knew?