Christmas Vegan burger

Name: Christmas Vegan burger
Cuisine: American, British, European
Ingredients: 1 tbsp olive oil; 1 white onion, small dice; 3 large garlic cloves, crushed; 200g mushrooms, chopped small; 2 sprigs fresh thyme, chopped; 1 sprig fresh rosemary, chopped; A pinch of nutmeg; Salt and pepper; 140g pre-roasted chestnuts, chopped; 1 tin drained chickpeas (240g drained weight); 1 tbsp tamari soy sauce; 40g oat, spelt or plain flour; 200g trimmed sprouts, halved; 1 red onion, in chunks; 1 tbsp balsamic vinegar; 1 tbsp maple syrup; 300g fresh cranberries; 50g agave or maple syrup; 120ml orange juice; 6 x Baker Street Burger Buns