Prepare the sous vide bath: Fill a stockpot or other food-safe container with water and insert an immersion circulator into the water bath. Set the temperature to 149ºF.
Make the pesto: In a food processor, combine the basil, parsley, walnuts, olive oil and salt. Process in 1-second pulses until it forms a smooth pesto, scraping down the sides of the container with a spatula as needed. Transfer to a bowl and set aside.
Butterfly and tenderize the chicken breasts: With a sharp knife angled parallel to the cutting board, slice into 1 side of the chicken breast until you are about ½ inch from the other side. Fan out the chicken breast on a piece of plastic wrap, and cover it with another piece of plastic wrap. Use a mallet or the back of a small skillet to flatten the chicken breast to an even thickness of about ⅓-inch. Repeat with the remaining chicken breasts.
Roll the roulades: Lay a sheet of plastic wrap on the cutting board. Place three slices of prosciutto flat on the plastic wrap, slightly overlapping each other. The prosciutto should be a wide enough layer so that the chicken breast can be placed in the middle, with about an inch border all the way around. Spread a ¼-inch-thick layer of pesto over the chicken breast, then roll it just as you would a cinnamon roll, using the plastic wrap to tighten the roll as you go.
When the roulade is fully rolled, close it up entirely in the plastic wrap, using enough to go around the roll at least 3 times (you can use another sheet if necessary). Twist the ends of the plastic wrap and tie them into knots as close to the roulade as possible, or use kitchen twine to secure the ends.
Drop the roulades into the water bath and let cook for 1 hour. When done, remove the roulades from the water bath, cut away the plastic and gently pat dry with a paper towel. Slice the roulades into 1½-inch slices and serve.