In a mortar, lightly crush the garlic with a pestle. Add the salt, oregano, cumin, and 1/2 tsp. black pepper and mash until a paste forms. Transfer to a medium bowl and add the lime juice, orange juice, and sugar; whisk until well combined. *You may also add all these ingredients in a food processor and pulse until well mixed.
Put the steaks in a ziplock bag and pour the garlic mixture (the mojo) inside. Seal the bad and lay it on a flat surface so that the steaks are covered in the mojo. Let the steaks marinate for no more than 10 minutes.
Meanwhile, heat the oil in a 12-inch skillet over high heat. Add the onions and peppers and cook, stirring constantly until they begin to soften, about 2 minutes. Transfer to a bowl.
Add the steaks to the pan along with 2 Tbs. of the mojo. Cook for 2 minutes, then flip the steaks and add the onions and peppers, cover and cook for 1 minute more. Uncover and continue cooking until the meat is just cooked through, about 2 minutes more.
Serve the steaks topped with the onions, peppers, and a drizzle of the cooked mojo.