Prep the shrimp. Use kitchen scissors to cut along the back of each shrimp, keeping the shell and head on. Remove the vein with a toothpick and rinse the shrimp clean if needed. Then run a knife lightly along the same cut to open it up just a bit more.
Prep the garlic. Crush garlic using a mortar and pestle. Set aside 1 tablespoon for the sauce. Use the rest for crispy garlic.
Make the sauce. In a small bowl, mix oyster sauce, light soy sauce, sugar, black pepper, and water.
Fry the garlic. Heat 3 tablespoons oil in a pan over medium heat. Add the garlic (not the reserved tablespoon) and fry until golden and crispy. Set aside.
Cook the sauce. In the same pan, sauté the reserved tablespoon of garlic in the leftover oil. Add the sauce mixture and simmer until slightly thickened. Set aside.
Cook the shrimp. Heat 2 tablespoons oil in a clean pan. Pan-fry the shrimp until just cooked on both sides.
Serve. Plate the shrimp, pour the sauce over, and spoon over the shrimp oil. Top with crispy garlic and serve with jasmine rice.