Brush tortillas on both sides with 1 tablespoon of the oil; sprinkle with half of the taco seasoning. Brush chicken breasts on both sides with remaining oil and sprinkle with remaining seasoning.
Coat unheated grill rack with nonstick cooking spray. Place tortillas on the prepared grill rack directly over medium heat; grill about 2 minutes or until crisp, turning once halfway through grilling. Transfer to four dinner plates. Place chicken on the rack of the grill directly over medium heat; grill for 12 to 15 minutes or until tender and no longer pink (170 degrees F), turning once halfway through grilling.
Divide spinach leaves and avocado slices among grilled tortillas. Shred chicken with a fork. Arrange shredded chicken over avocado. Spoon salsa over the chicken. Makes 4 servings.