Ingredients:

  Amount  Measure       Ingredient -- Preparation Method
--------  ------------  --------------------------------
   2      tablespoons   corn oil
   2      tablespoons   fresh lemon juice
   1      tablespoon    red wine vinegar
   1      teaspoon      crushed black pepper
   1      teaspoon      ground whole cumin seeds
     3/4  teaspoon      salt
   1      large         red onion
   3                    avocados -- 1/2" dice
   1      large         tomato -- diced
   2      cloves        garlic -- minced
   3                    serrano chilies -- chopped
   1      bunch         fresh cilantro -- chopped
                        fresh lime juice -- to taste

Preparation:

In a small bowl, combine oil, lemon juice, vinegar, pepper, cumin, and salt. Mix thoroughly. Peel and slice onion 1/4-inch thick and pour marinade over top. Marinate for 1 hour. Drain off liquid and lay the onion slices on a hot grill. Grill for 3 minutes per side. When done, combine with remaining ingredients in a medium bowl until thoroughly mixed. Taste for seasoning, and keep at room temperature until ready to serve.