Toast the sesame seeds in a dry pan over medium heat for 3 to 4 minutes, shaking the pan gently, until seeds are golden brown; remove from the pan at once to prevent burning.
Trim the ends from the spinach, roughly chop the leaves and wash to remove the grit.
Combine the garlic, spring onion, cayenne pepper and pork, mixing well. Heat the oils in a pan and stir-fry the pork quickly in three batches over very high heat until golden brown. Remove the meat and set aside.
Add the soy sauce, sugar and spinach and toss lightly. Cover and cook for 2 minutes or until the spinach is just soft. Return the pork to the pan, add the sesame seeds, toss well and serve immediately.