To prepare the kebabs, combine the first 5 ingredients in a large zip-top plastic bag. Add chicken to bag, and seal. Marinate in the refrigerator for 1 hour, turning occasionally. Add onion and zucchini to bag; toss well.
Remove chicken and onion mixture from bag; discard marinade. Thread chicken, onion, and zucchini alternately onto each of 8 (12-inch) skewers. Sprinkle kebabs evenly with 1/2 teaspoon salt and 1/4 teaspoon black pepper. Place kebabs on grill rack coated with cooking spray, and grill for 10 minutes or until chicken is done, turning occasionally.
To prepare raita, combine yogurt and remaining ingredients in a bowl, stirring well. Cover and chill. Serve with the kebabs.
Wine note: Onion is such a piquant, dominant flavor that it often makes wines taste hollow or dull. But sweet onions such as Vidalia or Maui pair wonderfully with a fresh, bold, well-chilled white wine. Given the mint and lemon in this dish, I would go for a lively sauvignon blanc. Many California sauvignon blancs have citrus and mint flavors, mirroring the flavors precisely, and the wine is dramatic enough to stand up to the flavor of onions. A great bet: Raymond Sauvignon Blanc Reserve 2005 Napa Valley, California ($14). --Karen MacNeil