Greek Salmon

Preheat oven to 375°. Marinate feta: In a large bowl, whisk together olive oil, lemon juice, garlic, oregano, and red pepper flakes. Season with pepper and add feta, tossing to coat. Cover and refrigerate for about 10 minutes while preparing other ingredients. Roast fish: Scatter the sliced lemon and red onion at the bottom of a large baking dish. Add salmon fillets, skin side down, to baking dish. Season with salt and pepper and bake until opaque and flaky, 18 to 20 minutes. Meanwhile, make topping: Into the bowl with feta, add tomatoes, olives, cucumbers, chopped red onion, and dill. Fold gently to combine. To serve: Plate salmon with lemon and red onion slices and top with feta mixture.