Combine yogurt, lemon zest, lemon juice, oregano (and/or marjoram), garlic, 1 tablespoon oil, ½ teaspoon salt and ¼ teaspoon pepper in a medium bowl. Transfer ½ cup of the mixture to a small bowl and refrigerate until ready to use.
Add chicken to the remaining yogurt mixture and stir to coat. Let marinate at room temperature for 20 minutes or refrigerate up to 1 day.
Preheat grill to high.
Toss bell pepper and onion in a large bowl with the remaining 1 tablespoon oil and ¼ teaspoon each salt and pepper. Thread the marinated chicken, bell pepper and onion pieces alternately onto eight 8- to 10-inch skewers. (Discard marinade.)
Reduce grill heat to medium. Oil the grill rack (see Tip). Grill the skewers, turning once, until the chicken is cooked through and the vegetables are tender-crisp, 6 to 8 minutes per side. Serve with the reserved yogurt sauce for dipping.
Make Ahead Tip: Marinate chicken (Step 2) for up to 1 day in the refrigerator; refrigerate dipping sauce separately.
Equipment: Eight 8- to 10-inch skewers
An oiled grill rack keeps your food from sticking. Once your grill is good and hot, dip a folded paper towel in a little oil, hold it with tongs and rub it over the rack.
291 calories;16 g fat(4 g sat); 2 g fiber; 10 g carbohydrates; 25 g protein; 23 mcg folate; 79 mg cholesterol; 7 g sugars; 0 g added sugars; 269 IU vitamin A; 41 mg vitamin C; 146 mg calcium; 2 mg iron; 545 mg sodium; 434 mg potassium