Heat 2 tablespoons of oil in a large skillet or wok over medium-high heat until almost smoking. Cook and stir the eggplant cubes, do not crowd working in batches, until they are brown, a couple of minutes. Remove the eggplant and set aside.
Heat 2 more tablespoons of oil in the skillet over medium-high heat,saute the onions until they begin to soften, a couple of minutes, do not brown.
Stir in the garlic, and cook a few more minutes. Mix in the soy sauce, water, GF teriyaki sauce, chili garlic sauce, agave, salt and black pepper, until smooth.
Return the eggplant to the skillet, lower the heat, and allow the vegetables and sauce to simmer until the eggplant is tender and almost all the liquid has been absorbed, about 5 minutes. Drizzle sesame oil over the dish, and give one final brief stir to combine.