Combine the peaches, brown sugar, lemon juice, and cinnamon in a saucepan. Cook over medium heat for 8 to 10 minutes until the peaches soften and the juices become syrupy.
Lightly mash half of the peaches, leaving the rest in small pieces. Transfer the mixture to a bowl and refrigerate until completely cold.
Line a 9 x 5-inch loaf pan with parchment paper, leaving enough overhang to lift out the frozen semifreddo.
Whip the chilled coconut whipping cream until it holds medium peaks. Fold in the condensed coconut milk, vanilla extract, and salt without deflating the cream.
Layer half of the cream mixture in the pan, followed by half of the peach mixture and half of the shortbread crumbs. Repeat the layers and gently swirl the top.
Cover and freeze for at least 8 hours. Let the semifreddo soften at room temperature for 10 minutes before lifting it from the pan and serving.