Add the cubed eggplant and the soyaki sauce to a mixing bowl and toss to coat. Place in the fridge to marinate for at least an hour - tossing every 15 minutes.
After it is done marinating, heat the sesame oil in a skillet over medium heat. Add the onion, garlic, ginger and eggplant - reserving the marinade in the mixing bowl. Allow to cook for a few minutes, or until the liquid in the pan is absorbed and the eggplant starts to brown.
Meanwhile, add the corn starch to the reserved marinade and mix until dissolved.
Toss the veggies, add the green onion and pour in the reserved marinade/corn starch mix. Toss until the sauce is thickened.
Serve the eggplant over rice and top with sesame seeds.
Video
Notes
Soyaki sauce can be subbed with Teriyaki sauce - look for one with sesame seeds in it for the most similar to soyaki. Start with 1/3 cup of sauce and add more if needed - this will depend on the size of your eggplant. The eggplant will absorb the sauce as it sits in the fridge and will also express water.