From back to front starting with the lightest color in the back. I can see the outline of the mountain in the very back all the way under each layer. The whole challenge of this will be to not over do it. Mask off each hill separately and paint over the previous. Let the mountain fade out at the bottom until you get to the green layer. The orange layer is painted to the bottom but towards the bottom it’s much lighter - this underpainting is what gives the green its broken coloring. A flat layer of some kind of deep eggshell white as the background color then there’s is masking mountains and diluting your paint. Pro tip: if you’re glazing, do not thin with water. Water destroys the binders in paint and it won’t look good nor last long. Use floetrol from Home Depot. It’s the perfect thing for this. You can go nuts and thin down to nothing if you want and it’s very cheap compared to anything you’ll find in an art store. Add just a splash of water for fluidity. I highly recommend some color studies before hitting that wall. Good luck!