Season the beef with salt and pepper and let it rest. Meanwhile, heat the oil in a pot. Sauté the onion until translucent, then add the garlic. Once fragrant, add the bell pepper, season lightly with salt and pepper, and cook until the pepper softens.

Add the beef and cook for a few minutes. Stir in the mustard, Worcestershire sauce, bouillon cube, and steak sauce or Maggi seasoning. Mix well to combine.

Add the mushrooms. Dissolve the cornstarch in 1/4 cup of water, pour the remaining water into the stew, then add the dissolved cornstarch. Stir everything together.

Simmer over medium heat for about 10 minutes. If the sauce is too thick, add a bit more water and adjust the seasoning as needed. Enjoy!