Preheat oven to 400. Layer 5 c. fresh spinach in the bottom of a 2 qt baking dish. Lay 2-6 oz filets atop the spinach. Scatter 10 cherry tomatoes, halved around the fish. Pour 1/2 c. vegetable broth into dish. Season fillet with 2 tbsp fresh dill, 1/4 tsp garlic powder, 1/2 tsp lemon pepper, 1/4 tsp onion powder, salt, and pepper to taste. Place 2 lemon slices, 2 onion slices, and 1 tsp butter on fish. Cover with aluminum foil. Bake 20 to 25 minutes or until the fish flakes easily.