Season chicken with salt and pepper. In a deep skillet with lid, heat oil over medium high heat. Cook chicken until golden brown, around 5 min per side. Pour tikka masala sauce over chicken. Bring to a simmer. Cover and reduce heat to medium low. Simmer for 20 min, turning the chicken once. Place chicken on cutting board and shred. Return chicken to pan, stir in tikka sauce that remains in pan.
While chicken simmers, mix the tzatziki sauce, chopped cilantro, coriander, and cardamom. Season with salt and pepper.
Warm tortillas or lightly char over gas flame.
Divide chicken between tortillas and top with tzatziki sauce mixture, onion and jalapeño. Garnish with cilantro.