In a large nonstick skillet, over medium high heat, melt 3 tablespoons of olive oil.
Once garlic begins to sizzle, add the mushrooms and season with 1/2 teaspoon salt.
Cook until mushrooms begin to wilt, about 6 to 7 minutes.
Add the scallions, thyme sprigs and butter and cook until the mushrooms are tender, another 3 to 4 minutes.
Transfer to a serving plate and keep warm, removing thyme sprigs.
Wipe out the skillet, return to medium high heat and add the remaining tablespoon of olive oil.
Season the scallops with remaining 1/2 teaspoon salt and cook, turning once, until just cooked through, about 1 to 2 minutes per side.
Serve on mushrooms, drizzled with balsamic vinegar if desired.