Not sure I'd go there, Opa; a lot of decomposing material does not a stable slipface make, and it doesn't address the slope. The ancient Chinese secret would be terracing; made all the easier by the modern miracle of landscape block (if you don't like the look, wallstone still works Or logs for a woodland garden). Build your soil inside the retaining wall, and use those dug trenches as footings for your wall. But simply digging trenches would make destabilizinng the slope face a possibility, just what we don't want to do.
I might even use the slope to full advantage and try alpine plants that appreciate sharp drainage and skip a good bit of the compost in favor of loam and sand...sedums, dianthus, and even odder beasties. Check this...