In a small saucepan over low heat, combine the cumin, garlic powder, onion powder, chile powder, and 4 tablespoons olive oil and bring to a light simmer. Cook for 4 minutes. Let cool. Place the steak in a baking dish and pour the seasoned oil over top. Marinate the steak in the refrigerator for 30 minutes. Bring the steak to room temperature before grilling.
Preheat a grill or grill pan on high heat.
Remove the steak from the marinade and season with salt and pepper. Grill the steak for about 7 minutes on each side for medium-rare. Let rest before slicing. Combine the onions and peppers with olive oil, and salt and pepper, to taste. Toss to coat in oil. Grill the onions and peppers for 4 minutes. Set aside.
Combine the avocado, red onion, tomato, garlic, lemon juice, and juice of 1 lime in a large bowl. Mash the avocado a bit with a fork. Stir in salt, and pepper, to taste. Mix in the sour cream with the remaining juice and zest of limes. Season with salt, to taste.
To serve: Slice the flank steak in thin slices and place it on a large platter. Serve with peppers and onions, guacamole, and lime-sour cream on the side.
This recipe was created by a contestant during a cooking competition. It has not been tested for home use.