Dietetic Chicken Stir-Fry

3 boneless, skinless chicken breasts
1 onion, chopped
2 medium zucchini, sliced
½ yellow pepper, thinly sliced
½ red pepper, thinly sliced
½ orange pepper, thinly sliced
3 large portobello mushrooms

Marinade:
2 garlic cloves, crushed
3 Tbsp light soy sauce
1 tsp salt
1 tsp black pepper
1 Tbsp dried basil
1 tsp Splenda (optional)

1. Cut chicken into bite-size pieces. Combine ingredients for marinade in a small bowl. Place chicken into a medium bowl and pour half of the marinade over it. Cover with plastic wrap and refrigerate for 2 hours.
2. Place the cut vegetables into a ziploc bag and add the remaining marinade. Mix well. Place the bag in the refrigerator for at least one hour.
3. Spray a large saucepan or wok with cooking spray. Place the chicken pieces into the pan for one minute. Stir well and let cook for 1 minute more. Remove from pan.
4. Empty the contents of the Ziploc bag into the pan and let the vegetables sauté for 6 to 8 minutes, stirring occasionally. Add the cooked chicken pieces and sauté on medium-high heat for 5 minutes more. Serve immediately.