Preheat oven to 220C/200C fan-forced. Line a large baking tray with baking paper.
Using your hands, combine mince, breadcrumbs, chilli, tarragon, allspice and cardamom in a medium bowl. Season with salt and pepper. Cover. Refrigerate until required.
Make Gluten-free pastry: Place flours, starch, xanthan gum and butter in a food processor. Process until mixture resembles breadcrumbs. With motor running, add egg and enough iced water so mixture just comes together.
Turn out pastry onto a lightly floured surface. Knead into a ball. Divide pastry into 3 equal pieces. Wrap 2 pieces in plastic wrap. Refrigerate until required. Roll remaining pastry between 2 sheets of baking paper to form a 15cm x 23cm rectangle. Shape 1/3 of the filling into a 23cm-long log. Place along centre of pastry. Gently roll up pastry from 1 long side to enclose filling. Cut into 4 pieces. Place sausage rolls, seam-side down, on prepared tray. Repeat with remaining pastry and filling. Brush tops of pastry with egg. Sprinkle with cumin seeds.
Bake for 15 minutes or until pastry is golden and filling is cooked through. Serve with tomato sauce.