In a small bowl, combine olive oil, garlic, salt, pepper and oregano. Adjust seasoning to your liking. Place the tomatoes cut side up on a baking tray. Spoon the olive oil mixture over the tomatoes and bake for 4-5 hours, until they reach the desired level of dryness . Let them cool completely, then transfer to a clean jar. Fill the jar with olive oil, making sure the tomatoes are completely submerged.
Keep the jar refrigerated and the tomatoes will last for at least a month.