For the Mojo:
12 cloves garlic (or 4 tablespoons minced garlic)
2 habaneros or other spicy chiles, cored, seeded, and minced (wear rubber gloves)
1 teaspoon kosher salt
4 teaspoons whole cumin seeds, toasted
1 cup olive oil
2/3 cup sour orange juice (or 1/3 cup fresh lime juice plus 1/3 cup fresh orange juice)
1 1/2 tablespoons sherry vinegar
salt and freshly ground black pepper to taste

For the Steak:
1 1/2 pounds flank steak
1 or 2 large Bermuda onions, thickly sliced and brushed with olive oil (optional)
salt and freshly ground black pepper to taste