Pat chicken cubes dry with paper towels and season with black pepper.
Heat olive oil in a large skillet or wok over medium-high heat until shimmering.
Add chicken to the skillet in a single layer and sear until golden brown and the internal temperature reaches 165°F, approximately 6 minutes.
Remove chicken from the skillet and set aside on a plate.
In the same skillet, add minced garlic and red pepper flakes; sauté for 30 seconds until fragrant, ensuring the garlic does not burn.
Add zucchini noodles to the skillet and toss constantly for 2 minutes until slightly softened but still firm (al dente).
Return the cooked chicken to the skillet.
Drizzle with soy sauce and sesame oil, tossing for 1 minute to emulsify the sauce and coat all ingredients.
Remove from heat immediately to prevent the zucchini from releasing excess moisture.
Garnish with sesame seeds and serve.