Beer-Marinated Flank Steak with Aji and Guacamole

From the July 2009 issue of Bon Appetit.
Makes 6 servings.

2- 1 1/3-pound flank steaks
1 tablespoon dried oregano (I used fresh oregano)
2 teaspoons cumin
Coarse kosher salt
1/4 cup extra-virgin olive oil
1 1/4 cup thinly sliced green onions (about 6)
1 12-ounce bottle dark beer
1/2 cup Worcestershire sauce

Aji Sauce (see recipe below)
Guacamole

Using sharp knife, lightly score flank steaks about 1/8 inch deep on both sides in a crisscross pattern at 1/2-inch intervals. Place steaks in 13x9x2-inch glass baking dish. Sprinkle steaks on both sides with oregano and cumin and generous amount of coarse salt and freshly ground pepper. Drizzle olive oil over both sides of steaks, rubbing oil and spices into meat. Add green onions, beer and Worcestershire sauce, turning steaks several times to coat both sides. Cover and chill at least 3 hours, turning occasionally. (Can be made 1 day ahead.)

Prepare barbecue (medium-high heat). Brush grill rack lightly with oil. Grill steaks to desired doneness, 3 to 4 minutes total per side for medium-rare, turning steaks 1/4 turn after 1 1/2 minutes to form crisscross grill marks, if desired. Transfer steaks to cutting board; let rest 5 minutes. Thinly slice steaks across grain. Transfer to platter and serve with Aji Sauce and guacamole.

Aji Sauce
Makes about 3/4 cup.

1/2 cup coarsely chopped seeded jalapeño peppers (about 4 large)
1/2 cup coarsely chopped green onions (about 2 large)
1/3 cup coarsely chopped sweet onion (such as Vidalia)
1/4 cup coarsely chopped fresh cilantro
2 tablespoons (or more) red wine vinegar or fresh lime juice
3/4 teaspoon coarse kosher salt
1/4 teaspoon freshly ground black pepper

Combine jalapeños, green onions, sweet onion, and cilantro in processor; puree until paste forms, scraping down sides of bowl with rubber spatula several times. Add 2 tablespoons vinegar (or lime juice) and process until mixture is blended but some texture still remains. Transfer to small bowl. Stir in salt and pepper and more vinegar or lime juice to taste, if desired. (Can be made 1 day ahead. Cover and refrigerate.)