Add the strawberries, sugar and salt to a small saucepan. Mix the cornstarch with 1/2 cup water in a small bowl and add it to the saucepan. Slowly heat the mixture over medium heat, stirring constantly, until it comes to a simmer, about 5 minutes. Lower the heat so it's at a very gentle simmer and cook, stirring frequently, until the sauce thickens, about 20 minutes. Remove from the heat, stir in the lemon zest and juice and let cool.
Serve over ice cream with salted peanuts on top.