Preheat a grill pan over medium heat with some olive oil in it.
Slice the scallion, peel, pit and slice the avocado. Put the sour cream or creme fraiche in a bowl.
Add the red onion to the grill pan and fry it for 2 minutes.
Add the bell pepper and fry for 2 minutes.
Flip both red onion and bell pepper and fry for another 2-3 minutes.
Tacke out of the grill pan.
Add the halloumi and fry for 1-2 minutes on each side, until grill marks start to form.
When the halloumi is done take it out of the grill pan and add the tortillas on at a time.
Fry for 20-30 seconds on each side, until grillmarks form.
Arrange the tacos by adding red bell pepper at the bottom. Then top with halloumi, red onion, scallion, avocado and cilantro. Serve with creme fraich or sour cream on the side.