Separate the fresh pho noodles and place them on a plate. Cover with plastic wrap and refrigerate for 30 minutes.

Slice the beef into bite-sized pieces. Marinate with 1 teaspoon seasoning powder, 1 teaspoon fish sauce, 1/3 teaspoon pepper, 1 teaspoon cooking oil, and 2 minced garlic cloves. Mix well and let it marinate for 20 minutes.

Peel and finely chop the garlic. Peel, wash, and cut the onion into wedges. Wash the Chinese broccoli, soak in diluted salt water for 10 minutes, rinse with clean water, drain, and cut into bite-sized pieces.

Heat 2 tablespoons of cooking oil in a pan. Add the pho noodles and stir quickly to separate. Add 1 tablespoon soy sauce and stir quickly to mix, then turn off the heat and transfer to a plate.

In the same pan, heat 2 tablespoons of cooking oil. Sauté half of the minced garlic until fragrant, then add the beef and stir-fry on high heat for 1 minute. Add the onion and stir for another 2 minutes, then turn off the heat.

In another pan, heat 2 tablespoons of cooking oil. Sauté the remaining minced garlic until fragrant, then add the Chinese broccoli. Season with 1 teaspoon sugar, 1 tablespoon oyster sauce, and 1 teaspoon fish sauce. Stir-fry until the broccoli is just cooked, then add the stir-fried beef and mix well. Adjust seasoning to taste, then turn off the heat.

Place the vegetables and beef on top of the pho noodles and drizzle with the stir-fry sauce. Serve hot with chili sauce or sliced chili soy sauce.