In a small bowl, whisk together miso, mirin, vinegar, garlic-chile paste, and garlic; set aside. Bring a large pot of water to a boil. Add soba and cook 7 minutes; drain and immediately transfer to a large bowl (some cooking water will cling to noodles). Add most of the scallions to noodles (reserve some for garnish) along with 2 tablespoons sesame oil; toss to mix. Cover to keep warm. In a medium nonstick skillet over medium-high heat, add remaining 1 tablespoon sesame oil. Add scallops and cook 2 minutes on each side, or until golden brown and opaque. Transfer to a plate and tent with foil to keep warm. Add miso mixture to skillet and cook over medium-high heat until bubbly, about 30 seconds. Pour sauce over soba noodles and toss to coat. Divide noodles among four shallow bowls and top each portion with scallops. Garnish with reserved scallions.