Heat the vegetable oil in a skillet over medium heat. Stir in the onion and garlic; cook and stir until the onion has softened and turned translucent, about 5 minutes. Stir in the sausage; cook and stir until the sausage is crisp. Mix in the rice, water, tomato sauce, adobo seasoning, salt, and black pepper. Bring to a boil, then reduce heat to low. Simmer until the rice is tender and the liquid has been absorbed, about 20 minutes.