Place 1 tablespoon of the olive oil, chili powder, ground cumin, paprika, cayenne, 1/4 teaspoon salt, and pepper in a small bowl. Mix well.

Pat the rub onto both sides of the flank steak, coating it as well as you can.

Place the beef in a non-reactive container (a Pyrex baking dish works well), cover, and place in the refrigerator. (This may be done 24 hours ahead if desired.)

Place the remaining 1 teaspoon olive oil in a large skillet over medium heat.

Add the diced onion to the skillet and saute the onion, stirring frequently, until it is starting to caramelize - 10-15 minutes.

Add the corn and jalapeno to the skillet.

Cook for 5 minutes, stirring frequently.

Add the green onions, red bell pepper, and 1/4 teaspoon salt.

Cook for 3 minutes and add 2 tablespoons beer. Stir frequently.

Cook for another 3 minutes until the liquid has evaporated. Remove from heat.

When almost ready to serve, turn on the broiler in the oven and place the beef, still whole, in the oven in a roasting pan or large skillet. (Line the pan or skillet with aluminum foil for easy cleanup.)

Broil the beef for about 6-8 minutes, then remove the beef from the oven, turn it over, and return to the oven for about another 6-8 minutes.

The beef is done when it reaches an internal temperature of 145F.

Remove the beef from the oven and allow to rest for 5 minutes.

When the beef is rested, slice the beef very thinly across the grain.

Prepare the tortillas by warming them on a skillet set on medium-high.

When they are pliable, divide the lettuce evenly between the 12 tortillas, then top with the steak.

Add the corn salsa and a dollop of sour cream to each taco.

Serve.