Separate any noodles that have stuck together, and set aside. If they are particularly stubborn, you can heat them in the microwave for 30 seconds or so.
Peel, smash, and roughly mince the garlic.
Cut the tofu into bite-sized pieces.
Slice the pak kana stalks into 1cm (½") strips, and the leaves into approximately 5cm (2") pieces.
Heat your wok over a high heat (the highest you can muster), and when it's hot, add the oil.
After a few seconds, once the oil is hot, add your garlic, and stir-fry for 10-15 seconds. It should be sizzling but not burning!
Add the tofu, and fry for 2-3 minutes.
Add the rest of the ingredients, and toss together for about 2 minutes.
Turn out into a bowl, and season to taste with chilli flakes, white pepper, and chilli vinegar.
When tossing the noodles, don't be too rough, or else you risk releasing a ton of starch, and them clumping together (this is also why you shouldn't stir pasta and rice while it's cooking!). If you're not used to cooking like this, then the easiest way is to use two wooden spatulas - wood is far more gentle than silicone or metal, both of which tend to have thinner edges, which makes it all too easy to bork the noodles!
Chilli flakes; some of you know that I invariably favour Korean red pepper flakes (gochugaru). They are far more flavoursome than regular chilli flakes, have a great colour, and aren't evil! If you want to use regular chilli flakes or grind up your own dried chillies, that's absolutely fine.
Chilli vinegar (nam som phrik dong); simply, vinegar with the addition of sliced chillies. One of the standard table condiments in Thai cuisine, which include white sugar, ground roasted chillies, crushed peanuts, phrik nam pla etc. These are used to season food and balance the flavours - just like having salt and pepper on the table in the West.