Zest the lemon then cut it in half. Juice one half and set aside then cut remaining half into 4 slices.
Heat a cast iron pan over medium heat with the 2 tablespoons of oil.
Season each salmon filet with 1/8 teaspoon salt, 1/8 teaspoon pepper, and lemon zest.
Place filets skin side down in the hot oil and leave for 4 minutes to allow skin to crisp. Place the lemon slices on top of each filet.
Flip when skin is crispy and move the lemon slices to the side to caramelize slightly, turning the heat down to low.
Remove the lemon slices as soon as they're starting to brown. Allow salmon to cook another 4-5 minutes or until 145°F. (Cook longer if you prefer a more well-done salmon).
Remove the salmon to a plate, keeping skin side up. Add the pasta to the boiling water.
Add the roasted garlic and let it cook into a paste. Then add the cream and slowly whisk in the milk.
When the cream mixture is steaming begin whisking in the cheese until it's all combine and melted. Allow to thicken at a very low simmer, stirring frequently.
Add the peas to the pasta water in the final 3 minutes of the pasta's cooking time.
When the sauce is thickened, begin whisking constantly while slowly streaming in 1/2 a tablespoon of lemon juice at a time. Taste after each addition until the lemon is to your liking. Season with salt and pepper to taste.
Add the drained pasta and peas to the pasta sauce and toss to coat.
Portion pasta with a filet, skin side up. Gently press juice out of caramelized lemon slice over top and serve.
Notes
*If you don't have roasted garlic, substitute 3 finely minced cloves of fresh garlic. Add to the pan at the same time, but stir constantly and cook for only 30 seconds before adding in the cream.