Prepare the tomato-cucumber salad by combining the tomatoes, onion, cucumber, olives, Feta cheese, and lime juice in a large bowl. Season with salt and black pepper, to taste, and stir to combine. Setaside.
Heat the olive oil and garlic in a large castiron skillet over medium heat. Add the lemon and capers and sauté until the lemon softens and develops a bit of color, approximately 2 minutes.
Add the grouper to the skillet and generously season with salt and black pepper. Cook for 3-4 minutes per side, or until the fillets are cooked through. (Cook time will vary depending on how thick the fillets are. The fillets are done when they flake easily with a fork).
Remove from heat and add the tomato-cucumber skillet to the skillet. Cover for 1-2minutes, or just until the cheese is softened and the other ingredients are warmed through. To serve, top with fresh thyme sprigs, if desired, and offer the lemon wedges on the side. Enjoy!
