Place the salmon, wrapped, in the freezer for approximately 10 minutes to help it firm up. If you are cutting from a larger piece and it is already well chilled, you can probably skip this, but it does make slicing easier especially if using all of a piece of fish.
With a thin-bladed sharp knife, very thinly slice the fish and place on either one larger plate to serve from or individual plates. Spread out the slices, slightly overlapping or arranged decoratively, as you like. If you won't be serving immediately, cover the plates and refrigerate at this point.
Mix together the lemon juice, orange juice, olive oil, sesame oil, soy sauce and ginger in a small dish so well blended (It will separate out a little but as best you can). Right before serving, drizzle the mixture evenly over the fish.
Sprinkle over the sesame seeds. Remove the cilantro leaves from the stem and place to sides or between slices of fish. Separate out the pieces of onion in the slice and scatter over the top then serve.
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Notes
Note quantities for all ingredients are approximate - adjust each to your taste. If you prefer a slightly more traditional flavor profile, you can skip the sesame oil, soy and ginger and simple use olive oil and citrus. Then I'd change the garnishes to be onion, capers and either basil or parsley.