Mix the gelatin with the water to soften.
Place the crushed pineapple and the orange juice in a small saucepan. Bring to a boil over medium heat.
Add the softened gelatin along with the sugar, lemon juice, orange extract and kosher salt. Stir until the gelatin has dissolved completely, about 10 minutes.
Let cool then chill until partially set, about 1 hour.
In a medium mixing bowl, whip the cream on medium speed for about 2 minutes to thicken slightly. Add the mascarpone cheese and continue beating until stiff peaks form, about 1 to 2 minutes.
Remove the gelatin from the fridge and gently fold the gelatin into the whipped cream.
Add the walnuts and the chopped orange.
Spoon the Bavarian into a serving bowl and chill until set, about 4 hours, or overnight.