Place the fresh udon noodles in boiling water, sit for 10 minutes, and drain.
Place a pan or wok over medium-high heat and add the Szechuan peppercorns, cumin seeds, and coriander seeds. Toast for 1 ½ minutes or until golden and cracking. Remove from heat and grind to a powder using a spice grinder or mortar and pestle.
Place the same wok over high heat. Add the garlic and stir fry for 40 seconds to 1 minute. Add the sliced beef fillet and stir fry for 2 ½ minutes. Add the ground spices and stir fry for another 1 minute.
Add the bok choy, soy sauce, and oyster sauce, stir to combine, and cook for 1 - 1 ½ minutes. Add the noodles, mix well until everything is incorporated, and add the chilli flakes (optional).
Remove the wok from the heat and serve in bowls. Garnish with thinly sliced spring onion (scallion), chilli flakes & coriander (cilantro). Dig in.