Preheat the oven to 375 degrees.
Pat the Mahi Mahi filets dry and season on both sides with salt and pepper. Drizzle with 2 tablespoons of the lemon juice and 1 tablespoon of olive oil. Set aside.
Heat the remaining 1 tablespoon of olive oil in a large (oven-safe) skillet over medium heat.
Add in leeks and garlic, a pinch of salt and a few grinds of black pepper. Sauté until the leeks begin to soften, about 5 minutes.
Using your hands, crush the tomatoes into the pan. Season with 1 tsp salt and a few grinds of black pepper. Let cook until warmed through and slightly thickened, about 5-7 minutes.
Place the fish on top of the tomato leek mixture & sprinkle the fennel seeds over top.
Transfer to the oven and bake until the fish is cooked through, tender and flakes easily with a fork, about 10-12 minutes.
Drizzle over the remaining lemon juice, garnish with fresh chopped parsley and serve warm.
