Heat oven to 350° F.
Finely chop enough onion to measure 3/4 cup and enough cilantro stems to measure 1 tablespoon (reserving the leaves).
Heat 1 tablespoon of the oil in an ovenproof skillet over medium heat. Add the onion, cilantro stems, and jalapeño and cook until softened, 4 minutes.
Pulse the cod, egg, salt, pepper, and the onion mixture in a food processor until combined but not pureed. Form 8 cod cakes. Coat each cake with the chips.
Wipe out skillet. Heat 1 tablespoon of the remaining oil over medium heat. Add 4 cakes and cook until golden brown, 3 minutes on each side. Transfer to a baking sheet. Wipe out skillet and repeat with 1 tablespoon of the remaining oil and the last 4 cakes. Bake until cooked through, about 10 minutes.
Thinly slice the remaining onion. Toss with the oranges, 1/2 cup of the cilantro leaves, and the remaining oil. Serve with the cakes.
Tip: Cilantro stems have a mild though distinct flavor. Use them when you want a slightly less pungent cilantro presence than you'd get from the leaves.