Add the vegetable oil to the wok and place over the highest heat possible.
Once the oil is hot, add the garlic. Stir-fry for 10 seconds.
Add the slices of pumpkin and coat in the oil and garlic. Stir fry for 20 seconds.
Add water until most of the pumpkin slices are half-submerged (judge this by eye rather than religiously adding half a wineglass). This is not an exact science (see 'cooking notes' for detailed guidance), but it is best to add too little rather than too much at this stage, as you can always top it up if it is getting too dry at any point. Also add the fish sauce, soy sauce and sugar.
Keep cooking, stirring occasionally, until the pumpkin is nearly soft enough to eat. To test this you can either eat a piece (my favourite method) or poke with your cooking spoon - if it easily goes through a piece of pumpkin then it is cooked. The amount of time it takes will depend on your wok and the size of your pumpkin slices. For thin slices it will probably be 1-2 minutes cooking in total. Remember to top up with a splash of water if it is getting too dry.
Once the pumpkin is nearly cooked, you are ready to add the egg. Make a well in the centre of the pumpkin with your spoon and crack it in. Break the yolk and slightly scramble with the spoon.
Cook until the bottom of the egg is turning opaque (20 seconds or so, around about the point in the above picture). Then stir the whole dish so that egg is mixed throughout.
If you are using Thai basil then throw in at this point.
Once the egg is cooked (a matter of seconds after the final stir) then the dish is done. Give it one final taste to make sure the pumpkin is cooked and the seasoning is correct. If there is not enough moisture, you can also add a splash more water.
Tip onto a serving plate.