Slice the chicken breasts into small bite-sized pieces. Wash the broccoli florets and mince the garlic.
Heat the olive oil in a large skillet or frying pan over medium-high heat. Add the chicken pieces and cook for 5–6 minutes, stirring occasionally, until the chicken is lightly golden and fully cooked.
Add the minced garlic to the pan. Stir and cook for about 30 seconds until fragrant.
Add the broccoli florets to the pan. Stir well and cook for 3–4 minutes until the broccoli is tender but still slightly crisp.
Pour in the soy sauce and sesame oil. Add the black pepper, salt, and chili flakes (if using). Stir everything together and cook for 1–2 minutes so the flavors combine.
Place the cooked rice or quinoa into a serving bowl.
Spoon the chicken and broccoli mixture over the rice or quinoa. Serve immediately while warm.