Drizzle a piece of aluminum foil about 2.5-3 times as wide as the piece of feta with a small dash of olive oil. Put a good pinch of salt and pepper on top.
Cut the onion into rings. Place half of the onion rings on the aluminum foil. Sprinkle with rosemary, thyme and a squeezed clove of garlic, depending on your taste. Place the feta on top and sprinkle with the remaining onion rings, garlic, herbs and spices.
Pour a dash of olive oil over it. Spread the tomatoes on the sides and seal the feta into a packet. Grill for about 15-20 minutes or bake in the oven at 200 ° C.