Heat oil in 10”-12” paella pan (or large skillet) over medium-high heat. Add onions and chorizo; cook until onions are tender and chorizo turns golden brown, about 7 minutes. Stir in garlic; cook until fragrant, about 30 seconds more.
Add 1 ¾ cups water to pan; bring to boil. Stir in contents of yellow rice mix and Alcaparrado. Boil rice mixture 1 minute; tightly cover pan. Reduce heat to medium-low; simmer 12 minutes. Add shrimp; simmer for about 13 more minutes, until rice is tender and water is absorbed.
Arrange pimiento strips over rice; sprinkle with parsley. Serve immediately.