Pre-heat oven to 350F. Line a small cookie sheet or baking dish with parchment paper, set aside.
Peel your orange with a vegetable peeler or a knife (just as you would a potato / apple). Keep the peel on the medium - thin size (i.e. no need to peel off deeply all the way to the actual orange). Then place the peels on a cutting board and cut into thin strips(like ⅛" wide or so, so you end up with long strips). Spread out on a the prepared baking sheet and bake in a pre-heated oven for 40 mins - hour, until the peel looks crispy and starts to brown up around the edges (time might vary depending on your orange slice thickness / oven temp steadiness, etc. so just keep an eye out until done. Remove from oven and cool off completely on a rack. The peels should be very crunchy (not leathery) once cooled -- if they're not, return to oven and bake longer. NOTE: alternatively you can dehydrate the peel overnight in a dehydrator instead.
Break up the peel into tiny pieces by hand. Set aside.
Melt your favorite dark chocolate bar (or see notes above for DIY alternatives) in a double boiler. While chocolate is melting, prepare a small metal tray / cookie sheet by lining it with parchment paper. Make sure the tray is at room temp. Once chocolate is melted, pour it out onto the parchment paper and allow it to spread out into a thin layer (can help it along with a spoon to even it out). Sprinkle with orange peel bits and almond slices, if using. Place in the fridge for 20 mins to set.
Once firm, break up into shards and enjoy. If you used tempered chocolate (i.e. most commercial chocolate bars), this should keep well at room temp, otherwise if you used a DIY chocolate or a raw chocolate for the base, you'll want to keep this refrigerated (or frozen for a crunchy bark -- that's how I love mine).