Line a greased 4 1/2-by-8 1/2-inch loaf pan with plastic wrap, leaving a 2-inch overhang. In a saucepan, bring 1/2 cup cream, the mint and jalapenos to a boil, then remove from the heat and let stand for 15 minutes. Strain; discard the solids.
In a double boiler, using a handheld electric mixer, beat the eggs, sugar and salt at high speed until tripled in volume and thick, about 8 minutes. Remove the bowl from the water and beat the mixture until cooled to room temperature, about 5 minutes. Mix in the jalapeno cream, chocolate and cinnamon; stir in the vanilla.
Using clean beaters, mix the remaining 1 cup cream until stiff peaks form. Fold about one-third of the whipped cream into the chocolate mixture, then fold in the rest. Spoon into the prepared loaf pan, cover and freeze until firm, about 5 hours.
Uncover the semifreddo and invert onto a chilled platter. Slice crosswise into 6 pieces and sprinkle with more cinnamon before serving.
