Heat a large heavy-duty skillet over medium-high heat until hot.
Add the olive oil and minced garlic to the pan and cook, stirring, for 30 seconds to 1 minute until fragrant but not browned.
Add the cut chicken pieces, red pepper flakes (if using), and a pinch of salt and pepper; cook, stirring occasionally, for 5–6 minutes until the chicken is golden and cooked through.
Add the spiralized zucchini to the pan, toss with the chicken for about 1 minute just to warm and soften the zoodles, then remove the pan from the heat.
Adjust seasoning with more salt and pepper if needed and serve immediately; sprinkle with parmesan cheese if desired.