1. Whisk together yogurt, lemon juice, garam masala, paprika, salt, black pepper, and cayenne in a small bowl.
2. Divide mixture between 2 large resealable plastic bags.
3. Place 5 chicken breasts in each bag, seal bags, and turn to coat chicken with marinade.
4. Lay bags flat in the refrigerator.
5. Refrigerate at least 2 hours or overnight.
6. Heat a grill or grill pan to medium-high.
7. Remove chicken from bags.
8. Brush grill with oil and grill chicken until cooked through, about 7 minutes per side.
9. Serve warm.
10. * make-ahead: Chicken can be marinated in resealable plastics bags in the refrigerator up to 1 day.