Ingredients

2 Sirloin steaks
2 Tbsp Worcestershire sauce
1 Tbsp Pepper
2 Tbsp Seven Colours Grill Seasoning^TM
1 Tbsp Oil 
25 g Butter
4 sprigs Thyme
1 clove Garlic, minced
2 Onions, sliced
2 Tbsp Brown sugar
1 Tbsp Balsamic vinegar
1 cup Mayonnaise
1 handful Parsley, minced
2 tsp Garlic paste
1 Tbsp Chilli sauce
2 slices toasted Baguette or any bread of your choice
2 handfuls Rocket

Method

Coat the steak with the Worcestershire sauce, then season with the pepper and 1½ Tbsp Seven Colours Grill Seasoning^TM. 
Add the oil to a preheated grill pan. Add the butter, thyme and garlic. Add the steaks and sear for 4 minutes on each side. Leave to rest for 5 minutes, then cut into slices.
In the same pan, cook the onion on low heat for 15-20 minutes, stirring, until softened and golden. Add the sugar and vinegar, and continue cooking on low heat for 5-10 minutes, stirring, until caramelised.
To make the sauce, mix the mayonnaise, parsley, garlic paste, chili sauce and remaining Seven Colours Grill Seasoning^TM. 
To assemble the sandwich, spread a thin layer of sauce on the toasted bread. Add a layer of caramelised onion, then some steak strips, then some rocket. Top with the remaining mayo sauce and the second slice of bread.
TIP: Serve immediately with sweet-potato fries.