Heat oil in 12” skillet over medium-high heat. Add onions and garlic. Cook, stirring occasionally, until soft and translucent, about 5 minutes.
Add contents of yellow rice mix and 2 cups water; stir to combine. Bring water to boil. Reduce heat to medium low. Simmer, covered, until rice is tender and water is absorbed, about 25 minutes, stirring in seafood medley, peas and pimientos after 15 minutes.
Remove pot from heat. Stir gently to combine. Serve warm.