Add the chicken to a medium sized mixing bowl. Sprinkle the cornstarch evenly out over them. Gently toss with a pair of tongs until the chicken pieces are all well coated.
Add the canola oil to a large skillet, or wok, set over medium high heat. Once the oil's hot (it will be shimmery), add the chicken.
Cook the chicken, stirring/tossing often, for roughly 6-8 minutes- until the chicken's nicely browned on all sides & cooked through. Using a flat skimmer, remove the chicken to a waiting plate. Set aside.
Reduce the heat to medium low, and add the minced garlic and ginger paste to the skillet. Stir them, cooking for 30-45 seconds- just until fragrant.
Add the mushrooms & zucchini to the skillet, stirring to combine. Rise the heat back to medium high, and cook them for 3-5 minutes stirring often- until fork tender, but not soggy and they've begun to brown.
While the veggies are cooking, whisk together the sauce. Add the soy sauce, vinegar, sugar, and sesame oil to a small bowl and whisk together until evenly incorporated.
Once the vegetables are ready, pour the sauce into the skillet. Quickly add the chicken back into the skillet, gently tossing everything to evenly coat and combine.
Continue cooking for another minute, just until the sauce has slightly thickened. Remove the dish from heat.
Serve the chicken and veggies with steamed white rice, and a sprinkle of sliced green onions & sesame seeds as garnish.