Heat oil in a large skillet over medium. Cook guanciale, tossing often, until browned and crisp, 6–8 minutes. Add shallots and garlic and cook, stirring occasionally, until softened, about 5 minutes. Add pepper and cook, stirring often, just until fragrant, about 1 minute.
Meanwhile, cook pasta in a large pot of boiling salted water, stirring occasionally, until al dente. Drain, reserving 1½ cups pasta cooking liquid.
Add pasta to skillet along with ½ cup pasta cooking liquid and 1 oz. Parmesan and toss to coat. Remove skillet from heat and add egg yolks. Toss again, adding more pasta cooking liquid as needed, until a smooth glossy sauce coats pasta. Add grated lemon zest, lemon juice, and another 1 oz. Parmesan. Toss to coat, adding more pasta cooking liquid if needed to loosen sauce.
Divide pasta among bowls; top with sliced lemon zest and more Parmesan.
Serving Size 1