For the walnuts, arrange walnuts in a dry nonstick pan over medium heat.

Sprinkle them with sugar, and cook until they are shiny and brown, 4 to 5 minutes, shaking the pan continuously.

Transfer to a small plate and set aside.

For the scallops, whisk together 2 teaspoons of the oil, tarragon, zest, garlic, shallots, and half of the lime juice in a wide, shallow dish.

Add scallops, toss to coat, cover and refrigerate for no longer than 30 to 45 minutes.

Add remaining 2 teaspoons oil to a large skillet over medium and heat for about 2 minutes.

Meanwhile, drain scallops from the marinade, and rest them on a paper towel for a moment to dry.

Gently add scallops to the skillet, trying not to crowd them together. Do not move them, as that makes the searing process more difficult.

Cook them on one side for 2 to 3 minutes, until the scallops are browned.

Turn them over, and repeat the process.

When the scallops are cooked through and opaque, deglaze the pan by adding the rest of the lime juice over the scallops.

Remove the scallops and the accumulated pan juices, and place them on a covered plate to keep warm.

For the spinach, heat oil in a large skillet over medium heat.

Add garlic and cook until just lightly browned.

Immediately add the spinach and cook briefly until the leaves are wilted.

Season with salt and pepper.

Form a nest of spinach on each of 6 plates.

Place a portion of the cooked scallops over the spinach, add a little of the pan juices, and top with the caramelized walnuts. Serve immediately.