Heat a wok until you can feel a good heat rising. Add 2 tbsp oil and, a few secs later, the garlic slices. Stir-fry until they start to turn golden, then using a slotted spoon, spoon onto kitchen paper to drain.
Toss in the pepper and stir-fry for 1 min or so until softened, then scoop out and set aside. Add the remaining tbsp oil. Heat, then toss in the prawns and stir-fry for another 2-3 mins until cooked and beginning to brown. Add the soy or fish sauce.
Throw in the spinach and stir-fry until it begins to wilt. Return the peppers and crisp garlic to the wok, then serve immediately.