In a medium saucepan melt 1/2 tablespoon butter over medium heat. Add rice and 1 teaspoon garlic; cook and stir 1 minute. Add stock, 1/2 cup water, and 1/4 teaspoon salt, and bring to a boil. Cover; reduce heat and simmer 15 minutes. Remove from heat. Let stand, covered, 10 minutes. Stir in peas and lemon zest.
Melt 1 tablespoon butter in a medium skillet over medium heat. Add remaining garlic and cook 30 seconds. Add shrimp and 1/4 teaspoon salt and cook until opaque, 5 minutes. Stir in 1 tablespoon lemon juice and 1/2 tablespoon butter. Cook 1 minute more and serve with pilaf.