• Preheat the oven to gas mark 4, 180°C, fan 160°C.
• In a shallow dish, whisk together the BBQ sauce and beer. Set aside. Put the onion in a bowl of cold water; leave to soak.
• Heat the oil in a heavy-based frying pan over a medium-high heat. Add the mushrooms, stalk-side down, and put a second, smaller heavy-based pan on top (make sure it's clean) to flatten them.
• Fry for 2 minutes, then flip the mushrooms, press down again with the smaller pan and fry for 2 minutes more. Season, sprinkle the spices over both sides of the mushrooms and fry for 2 minutes each side with the smaller pan pushed down on top.
• Add the mushrooms to the BBQ beer mix, turning to coat; leave to marinate for 15-20 minutes until cool. Brush a hot griddle pan with oil, then fry the mushrooms until lightly charred.
• Meanwhile, warm the taco shells in the oven for 2 minutes. Mash the avocado with the lime juice, chilli and a pinch of salt.
• Drain the onions. Slice the mushrooms into strips and divide between the tacos. Top with onions, lettuce, jalapeños and coriander.
• Serve with the avocado and a drizzle of BBQ marinade.

Recipe taken from Tesco Real Food