The trick to perfectly cooked salmon is to leave it alone. Once you add it to the pan, don't move it until it's ready to remove. By using this cooking method, you'll end up with a crispy top and juicy medium-rare to medium flesh at the bottom.
4 1-inch thick salmon fillets (about 6-ounces each)
1/2 teaspoon kosher salt
3 tablespoons olive oil
2 garlic cloves, thinly sliced
8 ounces baby arugula, rinsed and drained well
1 tablespoon red wine vinegar
1/4 teaspoon kosher salt
1/4 teaspoon black pepper
Season salmon fillets with 1/2 teaspoon salt, and allow them to rest at room temperature 15 minutes.
Heat olive oil in a large nonstick skillet over medium-high heat; carefully add salmon, skin side up. Immediately reduce heat to medium, and cook 3 to 4 minutes, covering skillet with lid after 2 minutes.
Remove salmon from skillet, set aside, and keep warm.
Remove all but 1 tablespoon of oil from skillet. Return to medium heat, and add garlic; cook 30 seconds, stirring constantly.
Add arugula and cook, tossing occasionally, until greens start to wilt (about 90 seconds).
Stir in vinegar and cook until it has almost evaporated, about 30 seconds. Season to taste with salt and pepper.
Divide arugula between 4 serving plates, top with salmon, and drizzle any remaining juices from pan over salmon.