Start by making the sauce. Place the sticky chilli sauce ingredients into your smallest saucepan and bring to the boil. Stir, and cook for a further 1-3 minutes until the sauce has reduced down to a runny syrup and then turn off the heat (it will thicker further as it cools).
Heat 1 tbsp of the oil in a skillet and fry the mushrooms with a pinch of salt and pepper until browned, then remove from the pan.
Add the remaining oil to the pan and heat.
Place the semolina on a small dish with a pinch of salt and pepper. Crack the egg into a small dish and whisk lightly with a fork.
Dip the halloumi slices into the egg, then coat in the semolina.
Place the coated Halloumi into the pan and fry on a medium-high heat for 2-3 minutes on each side – until golden brown.
Whilst the halloumi is frying, slice open and lightly toast the brioche rolls.
Place bottoms of the two brioche rolls on two plates and top with the lettuce and mushroom slices.
Once the halloumi is cooked, place it on top of the mushrooms. Top with slices of red onion and then drizzle over a little of the sauce. Place the top of the buns on the burgers and serve with any leftover sauce.