In a gallon-size sealable plastic bag, mix 1/2 cup of yoghurt, spice mix, lemon juice, oil, garlic and salt.
Add the chicken into it.
Seal the bag, squeezing out any air.
Refrigerate, turning the bag occasionally, at least for 6 hours or overnight.
Meanwhile, in a small bowl, mix the chutney and the remaining yoghurt.
Refrigerate, covered, until ready to use.
Preheat the broiler; line the broiler rack with foil and spray with nonstick cooking spray.
Transfer the chicken and the marinade to the rack.
Broil 6 inch from heat until cooked through and lightly crispy, 7 - 8 mins on each side.
Cool slightly, then cut into strips.
Heat tortillas according to package directions; spread with the yoghurt mixture.
Place the chicken, tomato and onion down the center of each tortilla; fold into bi-fold rolls.