Cut chicken into 3/4" cubes, fry in pan until cooked through, then drain. Return chicken to pan and add salsa approx. 1/2 a jar - enough to cover the chicken, heat through.
Leave tortilla shells on counter to room temperature or lightly steam them in the microwave to make pliable.
Spread onion and chive cream cheese in a 3" circle in the center of the tortilla, place a scoop of chicken and salsa on top of the cream cheese. Layer on Mexican/taco cheese mix, and wrap up tortilla shell so all ends are folded in.
Place chimichanga on baking sheet and bake for 5-10 min so cheese in side melts.