Add the thyme, onion, garlic, scallion, ginger, beef/all-purpose seasoning, salt and 1 tsp browning sauce to the beef strips and combine. Leave to marinate
Place a skillet pan with the cooking oil on medium heat and let it hot. Separate the marinade from the beef and add the beef strips to the cooking oil.
Stir until all the beef strips are brown on all sides.
Once all the beef strips are brown, add the marinade that you separated from the beef to the pan. Cook for 3-4 minutes.
Add the bell pepper, the rest of the browning sauce, beef broth and cornstarch. whisk the cornstarch in the beef broth before adding it to the pan. Leave to cook for another 5-7 minutes, until the sauce thickens.
Notes
You can use flank or round steak if sirloin isn't available.
If you find there is too much water from the meat in the pan, you don't have to add the beef broth. In this case, take some of the sauce from the pan to use to whisk the cornstarch, then pour it back in.