Boil water in a large pot and cook flat rice noodles according to package instructions until al dente. Drain and set aside.
Heat vegetable oil in a large skillet or wok over medium-high heat until shimmering.
Add minced garlic and sauté for about one minute until fragrant.
Add chicken or shrimp and stir-fry until cooked through (3-5 minutes for chicken; 2-3 minutes for shrimp).
Add bell peppers, broccoli, and carrots; stir-fry for 2 minutes until slightly tender but still crisp.
Return noodles to the skillet and add soy sauce and brown sugar.
Toss everything together until noodles are well coated and heated through.
Serve hot and enjoy your authentic Pad Kee Mao!