Preheat the oven to 375 degrees F. Place the potatoes in a large saucepan, cover with 1 inch of cold water, add 2 teaspoons salt and bring to a boil over high heat. Reduce the heat to medium and cook the potatoes until they are fork-tender, 5 to 8 minutes (depending on how big they are). Drain the potatoes and set aside until cool enough to handle; thinly slice the potatoes into rounds and set aside.
Heat a nonstick skillet over high heat. Add the grapeseed oil and cod and cook until browned, about 2 minutes. Transfer the fish to a large plate and set aside.
Arrange the fennel, garlic, potatoes, oregano, thyme, olives, capers and tomatoes in a medium broiler-proof casserole dish. Place the cod seared-side up and in the center of the dish and cover the cod with some of the vegetables. Drizzle with some olive oil and season to taste with salt and pepper.
Bake until the cod feels semi-firm to light pressure and the vegetables are caramelized, about 15 minutes. Heat the broiler to high and finish the fish under the broiler for 1 minute, until the crust is extra browned. Serve garnished with the parsley.