Preheat an oven to 450 degrees F (230 degrees C).
Rub the mahi mahi fillets with the olive oil and lay into a baking dish.
Bake in the preheated oven until the fish flakes easily with a fork, about 20 minutes.
While the mahi mahi bakes, melt the butter in a saucepan over medium heat.
Stir the garlic, lemon juice, and hot sauce into the melted butter; simmer together for 1 minute. Add the tomato and green onion to the butter mixture; cook and stir until hot. Spoon over the baked fish to serve.