Rinse quinoa, combine with water in a 1:1.75 ratio, and simmer 15 minutes; fluff with a fork.
In a shallow pan, bring water to a bare simmer with sliced ginger, the smashed garlic clove, and a squeeze of lemon.
Gently poach the cod in the aromatic water 8–10 minutes, keeping it at a bare simmer, not a boil.
Steam baby bok choy 3–4 minutes.
Serve the cod and bok choy over the quinoa, spooning a little of the poaching broth over the top.