In a measuring cup, thoroughly dissolve the cornstarch into an equal amount of chicken broth.
In a medium bowl, whisk the cornstarch and broth mixture together with the sugar, soy sauce, sesame oil, and the rest of the broth. Set asice
Over medium high heat, heat 1 tsp of cooking oil in a large pan or wok.
Add the vegetables to the pan and stir to coat evenly.
Cook for 5-6 minutes or until veggies are tender, stirring occasionally.
Remove from heat. Transfer the veggies to a plate and cover with foil.
Wipe the pan or wok clean with a paper towel. Add the rest of the cooking oil and return to heat.
Add the chicken and stir to coat evenly. Add salt and pepper to taste.
Cook for 3-4 minutes per side, until the chicken begins to brown and is cooked through.
Lower to medium heat, add the garlic, stir, and cook for 30 seconds.
Return the veggies back to the pan.
Quickly whisk the sauce again (it will probably will have started separating) and pour it over the veggies and chicken)
Bring to a simmer, lower the heat, and let simmer for 1-2 minutes or until the sauce begins to thicken.
Serve immediately.