Cut the sirloin steak into strips. Season with salt and pepper and Worcestershire sauce. Set aside while working on the aji amarillo paste.
Homemade Aji Amarillo Paste
Skip this step if you use premade paste. Cut the peppers open and separate the seeds from the peppers. Boil the peppers in a pot of water for 10 minutes. Take the peppers off the heat and blanche them (put them in ice water). Peel the outer skin off the peppers.
Slice the mango and put in a blender. Add the peppers to the blender as well. Add pepper seeds if you want a hotter paste. Blend until ingredients are well combined.
Cut the potatoes into french fry shapes. Heat up a large pot of vegetable oil. Flick a drop of water into the pot, if it bubbles and crackles heavily, add your potatoes.
Deep fry potatoes for 10 minutes, or until a little darker than golden brown. Salt them right after taking out.
Add vegetable oil to a large skillet and heat up. Add the sirloin strips. Cook until meat is nicely browned, about 6 minutes. Remove meat from skillet.
Add onion to skillet. Fry for 5 minutes, or until onion softens and has browning. Add tomatoes, garlic, and 3 tablespoons of your aji amarillo paste (2 if using premade). Cook for another 6 minutes.
Add soy sauce, parsely, and steak. Salt and pepper to taste. Cook for 1 minute.
Put French fries on the plate. Top with your stir fry. Put a scoop of rice on the side. Garnish with parsley.