Mushroom and Haloumi Burger

Ingredients

• 1 large Portobello or flat mushroom
• 1 ciabatta roll (or burger bun of your choice!)
• ½ brown onion, sliced thinly
• 2 lettuce leaves, chopped roughly
• 2 tomato slices, sliced thinly
• 60g haloumi, sliced thinly
• ¼ tsp chilli flakes
• ½ tsp chopped parsley
• 2 tbsp olive oil
• 1 tbsp whole egg mayonnaise
• 1 tbsp basil pesto
• Salt & pepper, to season