Heat oven to 350F. Butter a 9" pie pan. In pan, mix cherries with 1 tbsp sugar, lemon juice, and 1 tbsp flour.
In a food processor, pulse remaining 1/2 cup sugar, remaining 1/3 cup flour, pistachios, oats, walnuts, cardamom and salt until nuts are finely chopped, 1-2 mins. Stir in butter; sprinkle topping over cherries.
Bake until juices bubble thickly and topping is browned, about 25 mins. Serve warm or at room temp.