Remove fish from the refrigerator 15 - 30 minutes before you intend to cook it.
Preheat oven to 350 F.
To make the vinaigrette, mix 4 tbsp. of lemon juice, 8 tbsp. of olive oil, approximately 2 tsp of honey and season to taste with salt and pepper. Adjust the amount of honey and olive oil to balance out the acidity of the lemon.
Heat olive oil in a pan until just smoking. Make sure the fish is dry, season both sides with salt and season flesh side with pepper. Place in the pan skin side down and cook until the skin is crispy and the fish is nearly cooked through.
You will have to adjust the heat as you go to make sure that the skin gets crispy and brown without overcooking the fish. Turn the fish over and cook the fish side very briefly. Remove to wire rack.
Heat olive oil in a pan until it just begins to smoke and add the diced potatoes in one layer. Season with salt, toss and then let the potatoes sit until they begin to turn golden brown. Toss until they are somewhat evenly browned. If they need to continue cooking, put the pan in the oven and finish cooking in the oven.
Toss the butter, garlic, shallot and herbs into the pan and toss until the garlic and shallot are soft and fragrant. Add spinach and move it around vigorously until it is evenly wilted. Drain well.
Reheat the fish briefly in a hot oven and serve over the potatoes. Drizzle the vinaigrette over and around the fish.