Skewers: Thread the skewers starting with a tomato, then a piece of feta cheese, an olive, a piece of onion and finish with another tomato.
Vinaigrette: In a small bowl, mix together the lemon juice, red wine vinegar and oregano. Whisk in the olive oil until the mixture thickens. Season with salt and pepper, to taste.
Arrange the skewers on a serving platter. Spoon the vinaigrette over the skewers and sprinkle with the chopped oregano.