Bring a pot of water to a boil. Add the soba noodles and cook for 5-6 minutes until tender. Drain and rinse with cold water to prevent sticking.
In a small bowl, whisk together the miso paste, tamari, rice vinegar, toasted sesame oil, garlic powder, and ginger powder until the dressing is completely smooth.
Bring another small pot of water to a boil. Carefully lower the egg into the water and simmer for 7 minutes. Transfer to an ice bath for 2 minutes, then peel and halve.
In a non-stick skillet over medium-high heat, add the cubed tofu. Sear for 3-4 minutes per side until the edges are golden and crisp.
Add the broccoli florets and sliced mushrooms to the skillet with a splash of water. Cover and steam for 3 minutes until the vegetables are tender-crisp.
Stir in the fresh spinach and cook for 30 seconds until just wilted.
Place the cooked soba noodles in a serving bowl. Top with the seared tofu and the steamed vegetable mixture.
Drizzle the prepared miso dressing over the entire bowl and garnish with the soft-boiled egg halves before serving.