Blanch and Shock: Bring a large pot of water to a rolling boil, drop in your trimmed water spinach for exactly 90 seconds, then immediately plunge the hot greens into a prepared ice bath to stop the cooking process before draining them thoroughly and pressing out any excess water.
Pre-Mix the Sauce: Combine your fish sauce, oyster sauce, sugar, chicken bouillon, and a splash of water in a small bowl, stirring well until the sugar dissolves so that you don't have to scramble for ingredients while cooking over high heat.
Flash Stir-Fry: Crank your wok or skillet over high heat with a little neutral oil, toss in your minced garlic to sizzle for just a few seconds until it becomes highly fragrant without letting it burn, then throw in the blanched, well-drained morning glory and give it a rapid, aggressive toss.
Sauce and Finish: Pour your pre-mixed stir-fry sauce directly over the hot greens, toss everything together vigorously for 1 to 2 minutes until the vegetables are evenly coated and glistening, then finish by sliding in your sliced Fresno chilies for color before plating immediately to serve hot.