In a bowl, mix all the spices with the lean-cut beef and let marinate in the fridge for at least an hour.
Cut off the tips of the plantains and make a small cut in the peels to remove them.
Cut the plantains in half and then cut each section in half again lengthwise to make long and flat strips.
Pour 2 tablespoons of sunflower or vegetable oil in a pan over medium heat. When the oil is hot, add the plantain strips and fry until browned, about 3-5 minutes.
Once browned, pull the plantain strips out of the oil and press them down between two plates or with a heavy object to flatten them. Then place the flattened plantains in oil to fry again over high heat until crunchy, about 1-2 minutes.
Remove the plantain strips and let drain on paper towels to get rid of excess oil.
Preheat another pan on low heat, add 2 tablespoons of vegetable oil, and cook the meat until desired tenderness. The suggested time is 1-2 minutes for soft and juicy meat.
Whisk together the mayonnaise and ketchup and spread mixture on the plantain tops.
Top the plantain with steak, lettuce, tomato, cheese, onion, avocado, and a second plantain top. Now you have a crunchy and delicious Puerto Rican Jibarito sandwich!