In 12-inch nonstick skillet, heat oil over medium-high heat. Add pork; cook 4 minutes without moving. Cook 2 to 3 minutes longer, stirring occasionally, until no longer pink in center. Stir in 1 1/2 cups of the pineapple and 1 cup of the onions; cook 6 to 7 minutes longer, stirring occasionally, until onions soften and pineapple begins to brown. Stir in water and taco seasoning mix; heat to simmering. Reduce heat; simmer uncovered 2 to 3 minutes, stirring frequently, until thickened.