Mix cornstarch into 1 tsp cold water, stirring until dissolved, and set aside. Add broth and vegetables to a large frying pan and bring to a boil. Reduce heat and add maple, apple cider vinegar, soy sauce, juice, garlic, pepper and agave, if using. Cook for 5 minutes or until vegetables are cooked but still slightly crisp. Add cornstarch mixture and stir to combine. Turn up heat and wait for the sauce to thicken, but keep a watchful eye. Once the mixture is thick like a glaze, remove from heat. Garnish with sesame seeds if desired.