Skirt Steak Fajitas

1/4 cup olive oil 

1 small yellow onion, minced 

2 garlic cloves, minced 

3 Tbs. red wine vinegar  

1 tsp. chili powder 

1 tsp. ground cumin 

1 tsp. freshly ground pepper 

2 skirt steaks, about 4 lb. total, trimmed 

Salt, to taste 

8 large flour tortillas 

1/4 cup minced fresh cilantro  

2 cups guacamole homemade or purchased 

1 head lettuce, shredded  

1 cup fresh salsa  

1 cup pico de gallo  

1 1/2 cups shredded Monterey jack cheese  

1/2 cup crema or sour cream