How to make Chilean mouth-watering Churrasco Italiano Sandwich

Classic Chilean Churrasco Italiano Sandwich Recipe:
✅ 1 burger bun
✅ Butter
✅ 1 steak (300 g)
✅ Salt and freshly ground black pepper
✅ Vegetable oil for frying
✅ 1 avocado
✅ 4 tomato slices
✅ 3 tsp mayonnaise