Combine the baby arugula, avocado, tomatoes, and balsamic vinegar to a large salad bowl. Season with salt and black pepper, to taste, and toss to combine. Set aside.

Place a large cast-iron skillet over medium-high heat. Once hot, add the oil and swirl to coat the bottom of the skillet. Add the fish and cook for 4-5 minutes, or until it releases easily from the bottom of the skillet.

Turn the heat down to medium and flip each fillet. Cook for another 4-5 minutes, or until the fish is cooked through and flakes easily with a fork. Transfer to a platter and set aside.

Deglaze the skillet by adding the white wine and gently scraping the bottom with a plastic spatula to release the browned bits. Add the butter, lemon juice, zest, and thyme sprigs. Generously season with salt and black pepper, to taste, and stir to combine. Cook for 1-2 minutes, or until heated through. Remove from heat and discard the thyme stems in the sauce.

Briefly return the fish to the skillet to absorb some of the warm butter sauce. Transfer to individual serving plates and spoon some the pan sauce on top. Serve immediately with the avocado tomato salad topped with some crumbled Feta cheese, if desired. Enjoy!