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.