"This dish shows off the importance of contrasting textures and temperatures when assembling a dish. The hot, crisp-skinned salmon tops a warm, soft, earthy mushroom and potato salad; both are surrounded by a cool, tangy tomato citronette (vinaigrette made with citrus instead of vinegar). You'll be amazed how delicious the skin of the salmon gets when cooked this crisp!"
Place potatoes into a large pot and cover with salted water; bring to a boil. Reduce heat to medium-low and simmer until tender, 10 to 20 minutes. Drain and cut into bite-size chunks.
Cut 1/2-inch deep slashes lengthwise down the skin-side of each fillet. Season each fillet with salt and black pepper and rub 1/2 teaspoon olive oil into each.
Stir tomatoes, 3 tablespoons olive oil, 1/2 of the lemon juice, herb mustard, salt, and black pepper together in a bowl until well-combined. Cover the bowl with plastic wrap and refrigerate until chilled.
Heat 3 tablespoons olive oil in a nonstick skillet over medium heat. Cook and stir mushrooms and whole garlic clove over medium heat until mushrooms start to wilt, 5 to 10 minutes; remove garlic from skillet. Stir potato chunks, salt, and cayenne pepper into mushrooms; squeeze remaining lemon juice into skillet. Cook and stir until potatoes are crispy and golden, 10 to 12 minutes.
Heat remaining olive oil in a nonstick skillet over medium-high heat. Place salmon, skin-side down, in hot skillet and cook until fish is white about halfway up the sides, 5 to 6 minutes. Flip fish and cook until desired doneness is reached, 3 to 5 minutes more.
Divide potato-mushroom mixture between 2 plates and top each with a salmon fillet. Garnish with tomato mixture.