1In a bowl, mix the beef strips with the soy sauce, cumin, paprika, salt, and pepper. Let it marinate for at least 15 minutes.
Heat 1 tablespoon of olive oil in a large skillet over medium-high heat. Add the marinated beef strips and cook until browned, about 5-7 minutes. Remove the beef from the skillet and set aside.
In the same skillet, add the remaining tablespoon of olive oil. Add the sliced plantains and cook until they are golden brown and slightly crispy, about 5 minutes. Remove the plantains from the skillet and set aside.
Add the sliced onion, minced garlic, and bell pepper to the skillet. Cook until the vegetables are tender, about 5 minutes.
In a small bowl, mix the cornstarch with the water to create a slurry. Add the slurry to the skillet and stir well.
Return the beef and plantains to the skillet. Stir everything together and cook for an additional 2-3 minutes, until the sauce has thickened and everything is heated through.
Serve the Beef and Plantain Stir-Fry hot, garnished with additional salt and pepper if desired.