Heat 2 tablespoons oil in large skillet or Dutch oven over medium-high heat until hot. Add eggplant, zucchini, bell pepper, onion and garlic; cook and stir 8 to 10 minutes, or until tender. Place vegetables in bowl; set aside.
Sprinkle chicken with salt and pepper. Heat remaining 2 tablespoons oil in same skillet. Brown chicken in hot oil; drain. Add thyme, oregano and tomatoes. Bring to a boil. Reduce heat to low; cover and simmer 45 to 50 minutes or until chicken is fork tender and juices run clear.
With slotted spoon, place chicken on serving platter. Spoon 1 tablespoon tomato liquid from skillet into small bowl. Add cornstarch; blend until smooth. Add vegetable mixture to skillet. Stir in cornstarch mixture. Bring to a boil. Reduce heat; simmer uncovered 5 minutes. Pour over chicken.