Melt the butter in a large skillet over medium heat. Add the diced onion and cook until it softens, about 3 minutes.
Stir in the minced garlic and cook for 1 minute until fragrant.
Add the rice and stir to coat it in the butter. Toast the rice for 2 minutes.
Pour in the chicken broth, lemon zest, salt, and pepper. Bring the mixture to a boil, then reduce the heat to low, cover, and simmer for 15 minutes.
Scatter the shrimp and frozen peas over the rice. Cover again and cook for 5 to 7 minutes until the shrimp turn pink and the rice is tender.
Remove the skillet from the heat. Stir in the lemon juice and chopped parsley, then fluff the rice gently with a fork before serving.