Cook the brown rice noodles according to package instructions until al dente, then drain and set aside.
Pat the sirloin steak dry with paper towels and cut into 1-inch cubes, seasoning them evenly with sea salt and black pepper.
Heat a large cast-iron skillet or wok over high heat and add the ghee, allowing it to melt and coat the surface.
Add the steak cubes in a single layer and sear for 2 minutes without moving to develop a deep brown crust, then flip and cook for another 1-2 minutes until medium-rare.
Remove the steak from the pan and immediately add the sliced zucchini and onions, sautéing for 3-4 minutes until they are tender yet still crisp.
Lower the heat to medium and stir in the minced garlic and grated ginger, cooking for 30 seconds until fragrant.
Add the cooked noodles back into the pan along with the tamari and toasted sesame oil, tossing everything together until the noodles are well-coated and glossy.
Return the steak to the pan, toss briefly to combine all ingredients, and serve immediately garnished with sesame seeds.