Adjust the oven rack to 6 inches from the broiler element and preheat the broiler. In a large bowl, combine lemon juice, sugar, and salt. Toss in the peaches, ensuring they are well coated.

Place the peaches cut side up in a 10-inch oven-safe skillet. Pour any remaining sugar mixture into the peach cavities and add water around the peaches. Broil until the peaches begin to brown, about 11 to 15 minutes.

In a microwave-safe bowl, melt the raspberry jelly and butter (about 30 seconds), stirring to combine. Remove the skillet from the oven and brush half of the jelly mixture over the peaches. Return the peaches to the oven and broil until spotty brown, about 5 to 7 minutes.

Remove the skillet from the oven, brush the peaches with the remaining jelly mixture, and transfer them to a serving platter, leaving juices behind. Whisk the juices together and pour them over the peaches. Sprinkle with walnuts and serve.