2 small yellow onions
4 tablespoons extra-virgin olive oil, divided
2 tablespoons white or regular balsamic vinegar 
3 cups (packed) baby arugula (about 2¼ ounces)
½ pound large sea scallops, patted dry
½ ounce crumbled chèvre (goat cheese)
1. Cut onions into quarters; then thinly slice (or dice small). In a large, heavy skillet, heat 2 tablespoons oil over medium heat. Add onions and cook, stirring often, until golden and very soft, 15–25 minutes. (Reduce heat to medium-low if they start cooking too quickly.) Deglaze pan with balsamic vinegar. Season to taste with sea salt and freshly ground black pepper. Remove from heat and fold in arugula.
2. Sprinkle scallops with salt and pepper. Heat a second heavy skillet over high heat and add remaining oil; when very hot, add scallops and sear 1–2 minutes per side.
3. Mound onion mixture onto plates. Top with scallops and goat cheese.
PER SERVING: 405 cal, 28g fat (20g mono, 3g poly, 5g sat), 40mg chol, 22g protein, 13g carb, 2g fiber, 223mg sodium