How to Make It
Put the cod in a shallow baking dish and pat the sea salt all over it. Cover and refrigerate for 1 hour.
Meanwhile, peel the oranges with a sharp knife, removing all the bitter white pith. Working over a bowl, cut in between the membranes to release the orange sections into the bowl. Squeeze the juice from the membranes into the bowl.
Transfer 1/4 cup of juice to a bowl. Stir in 2 tablespoons of oil. Season the dressing with salt and pepper. Drain the orange sections; discard any remaining juice.
Rinse the cod thoroughly under cold water and pat dry. In a skillet, heat the remaining 1/4 cup of oil. Add the cod and cook over moderately low heat, turning once and shaking the pan to prevent sticking, until the cod is just cooked through and starts to separate into large flakes, 10 minutes. Transfer to a plate.
In a large bowl, combine the mesclun and basil leaves and toss with 2 tablespoons of the dressing. Transfer to plates and top with the orange sections and cod, separating the flakes slightly. Scatter the onion and red and green bell peppers over the salads, drizzle with the remaining dressing and serve.