Pat fish dry with paper towels. Sprinkle with salt and pepper on both sides. Heat 2 tsp olive oil in a 10-inch, nonstick skillet over medium-high heat. Add fish and cook for 2 to 3 minutes, or until edges start to brown. Carefully flip fish and cook about 2 more minutes or until fish is cooked through and flakes easily with a fork. Transfer fish to a serving plate, drizzle with lemon juice and keep warm. Wipe skillet clean and heat remaining 2 tsp olive oil over medium-high heat. Add onions and garlic. Cook and stir until onions begin to soften and garlic turns golden, about 2 minutes. Stir in tomatoes, vinegar and few grinds of salt and pepper. Mix well and cook 1 minute. Remove from heat and stir in feta and basil. Spoon warm bruschetta over fish fillets and serve immediately. Per serving: 201 calories, 6.8 g total fat (1.5 g saturated fat), 28 g protein, 6.8 g carbohydrate (1.8 g fibre, 3.7 g sugars), 63 mg cholesterol, 314 mg sodium