Heat olive oil in skillet or pan and add the sliced leeks. Season with salt and pepper and let the leeks cook at medium-high heat while stirring occasionally. Once the leeks start to soften and Caramelize, add the coconut milk, lemon juice, and lemon zest. Bring to a boil before turning the heat down to simmer. Add the rosemary and let the sauce simmer until the pasta is ready.