Preheat and Prepare: First, preheat your oven to 200°C (180°C fan). Lightly grease a 9x13 inch baking dish with a little butter or oil.

Pat the Fish Dry: Take your mahi-mahi fillets and pat them thoroughly dry with paper towels. This is a crucial step to ensure the fish bakes nicely rather than steams. Season both sides generously with salt and pepper.

Arrange in the Dish: Place the seasoned fillets in the prepared baking dish, leaving a little space between each one. If you're using them, scatter the cherry tomatoes and asparagus spears around the fish.

Create the Garlic Lemon Butter: In a small saucepan, melt the butter over a medium-low heat. Once melted, add the minced garlic and cook for about 1 minute until fragrant, but be careful not to let it brown.

Finish the Sauce: Remove the saucepan from the heat. Stir in the lemon zest, lemon juice, chopped parsley, and the optional white wine. Whisk everything together until combined.

Pour and Top: Carefully pour this beautiful sauce evenly over each fish fillet and the vegetables in the dish. I find that using a spoon helps to distribute it well. Arrange the thin lemon slices on top of each fillet.

Bake to Perfection: Place the dish in the preheated oven and bake for 15-18 minutes. The exact time will depend on the thickness of your fillets. The fish is cooked when it's opaque all the way through and flakes easily when gently pressed with a fork.

Rest and Serve: Remove the baking dish from the oven. Let the fish rest in the dish for 3-5 minutes. This allows the juices to redistribute, keeping the fillets succulent. Serve immediately, spooning some of the extra pan sauce over the top.