Place beef slices in a mixing bowl, then add half of the minced garlic, half of the salt, some black pepper, cornstarch and water. Toss well, then add 1 teaspoon cooking oil and give everything another toss. Set aside to marinate while preparing other ingredients.
Bring a large pot of water to a boil, then add the sliced green beans and julienned carrots. Blanch for a couple of minutes, then give them a quick rinse under cold water. Drain and set aside.
Heat a skillet over medium heat until hot. Add enough cooking oil to coat the bottom and then add the remaining minced garlic. Sauté briefly until fragrant.
Add the blanched vegetables to the skillet. Stir, then add the remaining salt and cook for 3-4 minutes or until they are crisp-tender or slightly past that stage. Increase the heat if needed. Transfer to a plate.
Maintain the skillet at medium-high heat and add the beef slices in a single layer. Let them sear undisturbed briefly, then add the oyster sauce. Stir and cook until the beef is still slightly pink, up to a minute.
Return the vegetables to the skillet. Stir-fry until the flavors meld and the beef is cooked through. Add the fish sauce and give everything a final toss. Adjust seasonings to taste.
Transfer the stir-fried green beans and beef to a serving plate. Sprinkle more black pepper and enjoy.