Sauce:
Preheat the oven to 450 F (230 C).

Season the cod with salt, pepper, and tarragon.
Put it in a dish and cook in the oven for 12 minutes or until the flesh starts to flake on the surface.

While the cod is cooking in the oven, put the shallots, tarragon, lemon zest, and broth in a saucepan, over high heat, and bring to a boil.
Reduce until only about 1/2 cup (125 ml) of sauce remains (about 5 minutes). Stir in the lemon juice and butter, and simmer. Season with salt and pepper.

Place the cod on four serving plates and spoon the sauce over it.

Sauteed Tomatoes and Zucchini with Basil and Pine Nuts:
Heat the oil in a large non-stick skillet over high heat.
Add the zucchinis and cook for 1 minute, stirring.
Add the tomatoes, onions, and vinegar.

Cook, stirring, for 1 or 2 minutes, or until the zucchinis are tender and slightly crunchy and the tomatoes are heated through.
Season with salt and pepper.

Sprinkle with basil and pine nuts, and serve immediately.