Place 1 cup pineapple juice, apple cider vinegar, ketchup, soy sauce, sugar and ginger in a small saucepan and bring to a simmer, whisking until sugar is dissolved. Whisk together remaining ¼ cup pineapple juice and corn starch in a small bowl. Whisk into the sauce and simmer until thickened, about 3-4 minutes. Taste and adjust seasoning, if necessary. Stir in pineapple. Set aside. Season chicken breast cubes with salt and pepper. Place corn starch in a medium bowl, add chicken to the bowl and toss to coat. Heat oil to medium-high heat in a deep skillet. Working in shifts, fry chicken in the hot oil for about 3-4 minutes, until golden brown, stirring occasionally to be sure chicken is evenly cooked. Remove using a slotted spoon and place on a paper towel. Once all chicken is cooked, toss with the sweet and sour sauce until coated. Serve pineapple chicken over rice with green onion.