Peel the lemon zest and divide it in half. Add half the lemon peels to the pasta cooking water along with salt and sugar.
In a food processor, combine the remaining lemon peels, 1 ounce of Parmesan, and the almonds. Pulse to a coarse paste.
Slowly add about ⅓ cup of olive oil while processing to make a pesto-like sauce.
Cook the pasta in the lemon-infused water for about 2 minutes. Reserve some of the cooking water before draining the pasta.
Toss the hot pasta with the lemon pesto, adding a bit of the reserved cooking water to emulsify the sauce.
Serve the pasta immediately, topped with additional Parmesan and optional scallions.
