For the mushrooms: In a saucepan over medium-high heat, add the olive oil to the pan and allow to heat until the verge of smoking. Then reduce the heat to medium and add the mushrooms. Allow the mushrooms to cook for 5 to 6 minutes, and then remove.
For the fish: In a nonstick saute pan, add the grapeseed oil over medium heat for 1 minute. Sprinkle the fish with salt and pepper, and then add the fish to the pan, flesh-side down. Cook for 2 minutes, flip the fish and turn the heat off. Allow the fish to finish with the residual heat for 2 minutes. Then remove the fish and allow to rest until serving.
For the sauce: In the same pan, return to medium-high heat. Sprinkle the tomatoes with salt and pepper, add to the pan and cook for 1 minute. Then flip the tomatoes and add the wine to deglaze the pan. Next, add the lemon juice, parsley and garlic. Remove the tomatoes and arrange flat on a serving plate, end to end. Allow the sauce to reduce by half, yielding 1/2 cup. Once reduced, turn the heat off and stir in the butter to finish the sauce. Then place the fish over the tomatoes, arrange the mushrooms and spoon the sauce over the fish. Serve.