How to Make It
Peel the orange with a sharp knife, removing all of the bitter white pith. Cut between the membranes to release the sections into a bowl.
In a nonreactive saucepan, boil the mirin, lemon juice, lime juice, soy sauce, ginger and coriander seeds over high heat until reduced to 3/4 cup, about 20 minutes. Add the orange sections and let cool slightly.
Light a charcoal grill or preheat the broiler. In a small skillet, stir the sesame seeds over low heat until lightly browned, about 1 minute.
Heat the 2 tablespoons olive oil in a large skillet. Add the garlic and cook over moderately high heat, stirring, until just golden, about 3 minutes. Add the pea shoots, season with salt and pepper and cook, stirring, until wilted, about 3 minutes.
Cut 3 or 4 shallow slashes in the skin of each mackerel fillet. Brush the fish lightly with olive oil and season with salt and pepper. Grill or broil the mackerel for about 2 minutes per side, or until the flesh just begins to flake. Sprinkle the fish with the toasted sesame seeds.
Mound the pea shoots in the center of 4 plates. Set the mackerel on the pea shoots and spoon the citrus sauce on top. Garnish with the cilantro sprigs and serve.