Steep the tea bags in 2 cups boiling water for 5 minutes. Remove the bags and allow the liquid to cool to room temperature.
Cut the chicken into bite-sized pieces. Put the pieces into a bowl and cover with the cooled tea. Cover with plastic wrap and refrigerate for 2 hours or up to overnight. When you are ready to cook, drain the chicken and pat it dry.
Heat 2 tablespoons canola oil in a large skillet or wok over medium-high heat. Add the ginger, garlic, and chicken and stir-fry until it is just cooked through, 4 to 5 minutes. Remove to a plate and set aside. Add the remaining 1 tablespoon oil to the pan, add the eggplant, and stir-fry until the eggplant begins to brown and soften, 3 to 4 minutes. Return the chicken to the pan, add the hoisin sauce and soy sauce, and stir-fry until the chicken is cooked through, 2 to 3 minutes.