For the sauce, in a medium bowl, whisk together the pineapple juice, soy sauce, brown sugar, ginger, garlic, sriracha and sesame oil. Set aside. In a small bowl, whisk together the cornstarch and water to form a slurry. Set aside.

Heat the oil in a large skillet over med-high heat. Once hot, add the chicken breast chunks to the skillet and season them with salt and pepper.

Cook until they are completely cooked throughout, about 5-7 minutes.

Pour the sauce over the chicken in the skillet and allow it to come to a simmer. Then stir in the cornstarch slurry. Simmer, stirring, for 2-4 minutes, until the sauce has thickened enough to coat the back of a spoon.

Remove from heat and serve, garnished with sesame seeds and scallions, if you'd like.