Slash the skin of the fish in a few places across the thickest part. This ensures that the fish does not curl, and cooks evenly. Sprinkle with salt.
Mix all the chermoula ingredients in a dish, and marinate the fish in half the quantity for about 30 minutes.
Slice the potatoes about 1/4 inch thick, and the tomatoes about 1/3 inch thick. Drizzle a bit of olive oil into a baking dish, put in the potatoes and tomatoes, and drizzle a bit more oil on top. Sprinkle with salt, then turn the vegetables so they are well seasoned and lightly coated with oil. Put the dish in a preheated 475ËšF oven for 50 minutes, or until the potatoes are tender. Turn the vegetables over once during cooking.
Remove the vegetables from the oven and place the cod fillets (skin up) on top; place the dish back in the oven and bake for 10 to 12 minutes more, or until fish is cooked through and flakes easily with a fork.
Just before serving, pour the remaining half of the chermoula over the fish, letting it dribble onto the vegetables.