Heat oil in medium, heavy pot over medium-high heat. Add onions. Cook, stirring occasionally, until soften and begin to brown, about 10 minutes. Add garlic and butternut squash. Cook, stirring occasionally, until garlic is fragrant, about 30 seconds more. Stir rice into pot. Cook, stirring, until rice is coated in oil, about 1 minute.
Pour 4 cups water and Adobo into pot; stir to combine. Bring liquid to boil; boil 1 minute. Cover pot; reduce heat to low. Simmer, covered, until rice and squash are tender and water is absorbed, 25 minutes.
Remove pot from heat; gently stir to combine. Serve warm.