Pre-heat the oven to 350 degrees. Rub chicken breasts on both sides with taco seasoning and place onto a lightly greased baking sheet. Place into the oven and bake at 350 degrees for 30 minutes or until the chicken breasts are fully cooked (the internal temperature has reached 165 degrees).
Remove from the oven, allow the chicken to cool for 10 minutes and slice into strips. In a blender or food processor add ranch dressing, salsa, lime juice and cilantro. Cover and process until smooth (this can also be done by hand, by whisking in a bowl). Set aside.
Turn the oven up to 425 degrees. Place the pre-baked crust onto a 12-inch pizza pan. Spread the ranch dressing mixture evenly over the crust. Sprinkle with the sliced cooked chicken, tomato, onion, and cheese.
Place into the oven and bake at 425 degrees for 17-20 minutes or until the crust is golden brown and the cheese has melted. Let stand 10 minutes before cutting. Sprinkle with lettuce and top with avocado slices. Serve immediately.