1. Heat a nonstick skillet or grill pan over medium-high heat. Coat fish with cooking spray. Add fish to pan, and cook 6 minutes on each side or until fish flakes easily when tested with a fork.
2. While fish cooks, pierce potatoes with a fork; arrange in a circle on paper towels in a microwave oven. Microwave on HIGH 8 to 10 minutes, rearranging potatoes after 5 minutes. Let stand 5 minutes.
3. Cut cooked potatoes in half, and sprinkle with salt, pepper, and cheese.
4. Combine greens, tomatoes, and vinaigrette in a bowl; toss gently.
5. Cut lemon in half, and squeeze lemon juice over fish. Serve with potatoes and salad.