In a medium mixing bowl, combine the teriyaki sauce, pineapple juice, pressed garlic, chopped green onions, and vegetable oil. Use a whisk to mix everything together until well combined.
Place the boneless, skinless chicken breasts in a large resealable bag or shallow dish. Pour the marinade over the chicken, ensuring each piece is well coated. Seal the bag or cover the dish and refrigerate for at least 30 minutes, but ideally for 2 hours or overnight for maximum flavor.
If you're grilling, preheat your grill to medium-high heat. For baking, preheat your oven to 375°F (190°C).
Remove the chicken from the marinade, allowing any excess to drip off. Grill the chicken for about 6-8 minutes per side, or bake in the oven for 25-30 minutes, until the internal temperature reaches 165°F (75°C).
Once cooked, remove the chicken from the heat and let it rest for about 5 minutes. This allows the juices to redistribute, ensuring each bite is tender and juicy.
Slice the chicken and serve it over rice, mixed greens, or in a wrap. Drizzle any remaining marinade over the top for an extra burst of flavor.