Preheat the oven to 375 degrees F (175 degrees C).
Grease a baking sheet with cooking spray. Place the tilapia fillets on the sheet, and coat them lightly with cooking spray. Spoon the melted margarine over each fillet, then drizzle with 2 tablespoons of lemon juice. Season with lemon pepper and 2 tablespoons of dill.
Bake for 15 minutes in the preheated oven, or until the fish is opaque and flakes easily.
While the fish is baking, combine the cream cheese, 5 tablespoons of lemon juice and 2 tablespoons of dill in a small bowl. Heat in the microwave for 1 minute and 10 seconds, then stir to blend.
Place fillets onto serving plates, and spoon sauce around them in a decorative fashion.