First, whisk together the cornstarch, water and canola oil in a small bowl. Add the chicken pieces to the bowl, and stir together until the chicken is completely coated. Cover with plastic wrap and set it in the fridge to marinate for 30 minutes while you chop all the vegetables.
Cook the rice according to package instructions
Stir together 1 tablespoon of reduced-sodium soy sauce, 1 teaspoon of sesame oil and ¼ teaspoon sugar in a small bowl and set aside.
Heat a skillet over medium-high heat and spritz it with nonstick spray. Cook the chicken in the skillet until the chicken starts to brown up. Set the chicken aside on a plate.
Heat 1 teaspoon canola oil (or any other neutral-tasting oil) over medium-high heat in the same large skillet. Add the minced garlic and grated ginger and stir them around for about 30 seconds. Try to scrape up any browned chicken bits still stuck to the pan, as this will add more flavor.
Next, add the shallot, the white parts of the green onion, the red bell pepper and carrot to the skillet and cook until the vegetables start softening.
Add the cabbage, summer squash, water chestnuts and walnuts. Put a lid on the skillet, turn the heat down to medium-low and steam the vegetables for 5 minutes or so, until the cabbage is tender.
Add the chicken back into the vegetable mixture. Pour in the sauce mixture, and mix it all together. Make a pile of rice on each serving plate and scoop the stir fry mixture on top.