Heat a wok or large frying pan over high heat and add the oil.
Add the minced garlic and stir-fry briefly until fragrant, about 15–30 seconds.
Add the Thai roasted chili paste (nam prik pao) and stir to combine with the garlic.
Add the sliced chicken and stir-fry over high heat until the chicken is about half cooked, about 2–3 minutes.
Add the onion, green beans, carrot, green and red bell peppers, and the lightly pounded chilies (if using). Stir-fry together until the vegetables are crisp-tender and the chicken is cooked through, about 3–5 minutes.
Stir in the sweet soy sauce and fish sauce and toss to coat everything evenly. If you prefer a slightly saucier dish, add 2 tablespoons of water and stir to combine.
Cook another 1 minute to let the flavors meld, then remove from heat and serve immediately with steamed rice.