Creamy Vegan Pumpkin Chestnut Pasta

2 portions pasta (ensure gluten-free if necessary) Handful of kale For the pumpkin sauce: 2 tablespoons oil (olive, coconut, rapeseed or vegetable oil) 1 onion, diced 1/2 teaspoon dried sage (or sub equivalent amount fresh sage) 90 g (3oz) pumpkin purée (either store-bought or make your own by boiling/roasting pumpkin and blending until smooth) 120 ml (1/2 cup) unsweetened almond milk (or sub oat milk for nut-free version) Salt + pepper, to taste Handful of chestnuts, roughly chopped