In a small bowl, combine salt, pepper, thyme, orange zest, and olive oil. Add red wine and mix well. Place in plastic bag with monkfish, seal and marinate in the refrigerator for 24 hours.
Preheat the oven to 350 degrees F. Heat the butter in a nonstick pan. Add the garlic and saute in butter until lightly golden. Add mushrooms and cook until the water has evaporated. Season with salt and pepper and cool.
With an apple corer, make a hole lengthwise through the potato saving the core. Fill the potato with enough mushroom filling to pack the inside of the potato. Cut the ends of the cores off and use as caps to seal off the ends of the potato. Rub olive oil, salt and pepper on the potatoes. Wrap in foil and bake for 45 minutes.
Prepare sauce by reducing red wine, balsamic vinegar, shallots, and bay leaf until lightly thickened. Add the veal stock and bring to a simmer. Strain, whisk in cold butter and season with salt and pepper.
Remove fish from the marinade. Pat dry and season with salt. In a large skillet, heat 4 tablespoons olive oil until very hot over high heat. Add fish and brown on all sides. Finish cooking in the oven until fish is cooked through, about 8 to 10 minutes
Saute spinach with olive oil in a large pan until wilted and season with salt and pepper.
Place the spinach in piles in the center of 2 large plates. Place the fish around the spinach at the12 and 6 o'clock positions. Cut potatoes on the bias trimming the ends to lay flat and place at 9 and 3 o'clock positions. Pour the wine sauce over the fish and serve.