1. Line a colander with a double layer of cheesecloth or four layers of paper towels; set colander in a sink or over a large bowl. Empty yogurt into lined colander and let drain about 30 minutes.
2. Meanwhile, rinse, stem, and seed bell pepper; cut into 1-inch squares. Peel onion and cut into 1-inch chunks, separating layers. Cut pineapple into 1-inch chunks. If using chicken, rinse and pat dry. Cut chicken, cheese, or tofu into 1-inch chunks.
3. In a large bowl, mix drained yogurt with tandoori masala. If using chicken, scoop out 1/2 cup yogurt mixture and combine with chicken in a small bowl. Gently mix bell pepper, onion, pineapple, and cheese or tofu, if using, into yogurt mixture in large bowl. Cover and chill at least 30 minutes or up to 2 hours. Thread vegetables, pineapple, and chicken, cheese, or tofu onto metal or soaked wooden skewers, alternating items.
4. Lay kebabs on an oiled grill over a solid bed of hot coals or high heat on a gas grill (you can hold your hand at grill level only 2 to 3 seconds); close lid on gas grill. Cook, turning once, until vegetables are browned on both sides and chicken is no longer pink in the center (cut to test), 8 to 10 minutes. Transfer to a platter. Serve hot or warm, with raita to add at the table.
Tandoori masala: In a small bowl, combine 1 teaspoon each ground cumin and ground coriander, 1/4 teaspoon each ground cloves and cayenne, and 1/8 teaspoon each ground nutmeg, ground pepper, and ground cinnamon; mix well.
Raita: In a bowl, mix 3/4 cup plain nonfat yogurt with 1/2 teaspoon each ground cumin, sugar, and salt. Gently stir in 1/4 cup each finely chopped cucumber, tomato, and onion. Makes about 1 1/4 cups.
Nutritional analysis per serving with chicken.