Start by preheating your oven to 400°F (200°C). Wash and dry the cherry tomatoes thoroughly. Slice the onion and mince the garlic so everything is ready to assemble quickly.
Place the cherry tomatoes and sliced onions in a baking dish. Add garlic, olive oil, oregano, red pepper flakes, salt, and pepper. Toss everything gently to coat evenly with the oil and seasoning.
Nestle the block of feta cheese right in the center of the vegetables. Drizzle a little olive oil over the feta to keep it moist while baking and enhance its golden finish.
Transfer the dish to the oven and bake for about 25 minutes. The tomatoes will soften and burst, and the feta will become warm and slightly golden on top.
Remove from the oven and sprinkle fresh basil and lemon zest over the top. Give everything a gentle mix if desired, or serve as is with crusty bread.