3
Jelly, 13 bytes
ạ/S’
2ṗœc2ÇÐḟ
Try it here. For input 3, the output is:
[[[1, 1, 1], [1, 1, 2]],
[[1, 1, 1], [1, 2, 1]],
[[1, 1, 1], [2, 1, 1]],
[[1, 1, 2], [1, 2, 2]],
[[1, 1, 2], [2, 1, 2]],
[[1, 2, 1], [1, 2, 2]],
[[1, 2, 1], [2, 2, 1]],
[[1, 2, 2], [2, 2, 2]],
[[2, 1, 1], [2, 1, 2]...