Add olive oil to a skillet over medium heat and brown the chicken on all sides, about 8 minutes. Remove the chicken and set aside. Add broccoli florets and lightly sauté until slightly tender. Remove broccoli and set aside.
Add the onion and celery to the skillet and cook for 5 to 8 minutes, until the celery has softened, and the onion is translucent. Add the garlic and cook for 30 seconds, until fragrant. Add the broth (or water), chicken, and broccoli back to the skillet along with the salt and pepper. Cook ingredients for about 5 more minutes, until chicken is heated through.
For sauce, whisk together ingredients and add to the pan for the last minute of cooking time. Serve and enjoy!