1. Heat the chicken broth in a saucepan and keep it warm.
2. In a large skillet, heat olive oil and butter over medium heat. Add the onion and garlic, and cook until softened.
3. Add the Arborio rice to the skillet and cook, stirring constantly, until the rice is lightly toasted.
4. Begin adding the warm broth one ladle at a time, stirring frequently until the liquid is absorbed before adding more.
5. Continue this process until the rice is creamy and cooked through, about 20 minutes.
6. Stir in the shrimp, lemon zest, and lemon juice. Cook until the shrimp are pink and cooked through, about 5 minutes.
7. Remove from heat and stir in the grated Parmesan cheese. Season with salt and pepper to taste.
8. Serve immediately, garnished with additional lemon zest and Parmesan if desired.