Preheat the oven to 350°F (175°C).
In a small bowl, combine the lemon Jell-O (3 oz), melted butter, prepared mustard, garlic salt, and a pinch of black pepper; mix until smooth.
Place the chicken breasts in an ungreased baking dish and brush the Jell-O mixture evenly over both sides of each piece.
Sprinkle the thinly sliced almonds over the coated chicken breasts.
Cover the dish and bake at 350°F for 20–25 minutes, basting once during baking.
Remove the cover and bake uncovered for about 15 minutes more, or until the chicken is cooked through and juices run clear (internal temperature 165°F).
Let the chicken rest a few minutes before serving; serve with rice if desired.