Season the beef cubes with salt and black pepper.
Heat the vegetable oil in a large skillet or grill pan over medium-high heat.
Add the beef cubes and cook until browned on all sides, about 5-7 minutes. Remove the beef from the pan and set aside.
In the same pan, add the chopped onion and cook until softened, about 3-4 minutes.
Add the minced garlic and cook for an additional minute.
Stir in the diced tomato, green bell pepper, and red bell pepper. Cook for another 5 minutes, or until the vegetables are tender.
Add the paprika, ground cumin, ground coriander, and cayenne pepper (if using) to the pan. Stir well to combine.
Return the browned beef cubes to the pan and mix with the vegetables and spices. Cook for another 5-10 minutes, or until the beef is cooked through and well-coated with the seasoning.
Garnish with chopped fresh cilantro or parsley.
Enjoy your meal!