1. Preheat a wok or large skillet on low. In a bowl, combine chicken broth, vinegar, soy sauce and brown sugar. Turn heat up to high. Pour in 1 Tbsp. canola oil and, once hot, add half of chicken and sauté until cooked through, about 5 minutes. Remove to a plate. Repeat with 1/2 Tbsp. oil and remaining chicken.
2. Add vegetables and 1 1/2 Tbsp. oil to wok; sauté until tender, about 3 minutes. Add garlic; sauté 1 minute.
3. Return chicken to wok; add pineapple, if desired. Pour in chicken broth mixture and stir well. Add cornstarch and stir until sauce thickens and becomes shiny. Serve over brown rice or whole-grain noodles.