Remove the core from the tomatoes and slice each tomato in thick wedges. Arrange the tomatoes in a circle on a large plate. Cut the feta in thick slices and place it in the center of the plate. Drizzle the olive oil and vinegar over the tomatoes and feta. Crush the oregano between the palms of your hands over the salad and sprinkle with the salt and pepper. Arrange the arugula on the plate around the outside of the tomatoes and serve at room temperature.