In a medium bowl or measuring cup, whisk together the reserved pineapple juice, chicken broth, soy sauce, honey and cornstarch until smooth.
In a skillet, heat 1 tablespoon of the oil over medium-high heat; saute the chicken until lightly browned, 4 to 6 minutes. Remove the chicken from the pan and set aside.
In the same pan, saute the bell pepper, onion, ginger, garlic and red pepper flakes in the remaining oil until crisp-tender, about 2 minutes. Give the cornstarch mixture another stir, and then add it to the pan along with the chicken and pineapple chunks. Bring to a boil, stirring constantly. Cook and stir until the sauce has thickened and the chicken is cooked through, 5 to 7 minutes.
Serve over rice (if desired) and sprinkle with fresh cilantro (if desired).