Mix salt, black pepper, garlic powder, and flour in a bowl.
Coat the sirloin steak pieces with this dry mixture.
Heat olive oil in a skillet over medium heat.
Add the coated steak pieces and cook until browned on all sides.
Remove steak pieces and set them aside.
In the same skillet, add onions and mushrooms and cook until soft.
Pour beef broth into the skillet and stir well, scraping up the browned bits from the bottom.
Return the steak pieces to the skillet.
Reduce the heat to low, cover, and let simmer for 15-20 minutes until the sauce thickens.
Serve hot.