Black bean veggie burger

Name: Black bean veggie burger
Ingredients: 1 tbsp olive oil, for frying; ½ leek, chopped; 5 mushrooms, chopped; 30g thyme, leaves picked; 140g firm tofu, chopped; handful of kale leaves; 1 tbsp Dijon mustard; 2 tbsp tamari; 240g canned black beans, drained; 3 tbsp oat bran; 2 tbsp cooked brown rice; 2 tbsp chopped hazelnuts or walnuts; 40g gram flour (optional); 4-6 burger buns; 4 tbsp vegan mayo; 1 tsp tomato ketchup; 1 tbsp chopped cornichons; pinch of cayenne pepper; sliced tomatoes and red onion; lettuce leaves