Stir the chili garlic sauce, soy sauce, sugar, and cornstarch slurry together in a small bowl. Park it next to the stove. Once the wok is hot there is no time to measure.
Pat the shrimp very dry with paper towels and season with a small pinch of salt. Dry shrimp sear, wet shrimp steam.
Heat 1 tablespoon of oil in a wok or large skillet over the highest heat your stove has, until the oil just starts to smoke. Add the green beans and stir fry 3 to 4 minutes until blistered and spotted brown. Tip them onto a plate.
Add the remaining oil. Lay the shrimp in a single layer and leave them alone for 1 minute, then toss for another minute until they are just turning pink.
Push the shrimp up the sides, drop the garlic into the middle, and stir 20 to 30 seconds until fragrant but not browned.
Return the beans, pour the sauce in around the edge of the wok, and toss 30 to 60 seconds until everything is glossy and the sauce clings. Serve immediately, over rice if you like.