Cook your spaghetti to almost al dente. The rest takes about 5 minutes to do so time appropriately
Heat the oil in a large pan on medium heat, then add garlic and pepper flakes. Saute for 2 minutes until garlic darkens and becomes fragrant.
stir in the lemon juice, scraping up any fond that's formed with a spatula or flat bottom spoon
Once your pasta is done, strain it reserving 1/4 cup of water
turn the heat to low and whisk in the pasta water and parmesan. Whisk continually until the parmesan has fully melted in, 1-2 minutes
Add the pasta to the pan and toss with tongs til fully coated
Add in the parsley and pepper to taste, then toss for another couple seconds til integrated
Serve with more fresh parsley to garnish