Soak 12" wooden skewers in water overnight. In a mixing bowl combine lamb cubes, olive oil, garlic, oregano, salt, and pepper. Let marinate for a minimum of 2 hours or preferably overnight. To assemble kabobs, skewer a cube of zucchini, lamb, scallion, yellow tomato, lamb, red tomato, and push tightly together and repeat the pattern until skewer is full. Brush with lamb marinade and then place over medium hot fire, turning 2-3 times and cook for 5-8 minutes, occasionally brushing with lamb marinade and turning every few minutes until cooked. Remove from fire, plate, and serve with Feta Tabbouleh and Tzadziki Sauce.