Slice the beef into long, thin strips.

In a glass dish, mix together the olive oil, vinegar, seven spice, black pepper, salt, and the juice of the lemons. Stir well, then add the beef. Add the chopped tomatoes and onions, and mix. Cover and refrigerate for several hours.

Preheat the oven to medium heat. Place the mixture in a baking dish and bake for 1 1/2 hours.