In a medium pot of boiling water, cook noodles according to package instructions. Drain noodles and place in a bowl of cold water. In a medium nonstick skillet, heat vegetable oil over medium-high. Add mushrooms and cook, stirring occasionally, until soft, about 4 minutes. Add scallion, ginger, and garlic and cook until fragrant, 1 to 2 minutes. Drain noodles and add to skillet along with spinach. Toss until spinach wilts and noodles are warmed through. Add soy sauce and sesame oil and toss to combine.
Use rice noodles and swap tamari for soy sauce for a gluten-free version.