Preheat a nonstick grill pan over medium heat. Thread 1 skewer with 1 whole tomato, 1 zucchini round, and 1 beef cube. Repeat two more times, ending with a tomato. Thread the remaining tomatoes, zucchini rounds, and beef cubes onto the other skewer. Drizzle the skewers with the remaining 1 teaspoon oil, turning to coat both sides. Season with salt and pepper.