Combine the olive oil and garlic in a large shallow baking dish. Add the flank steak and turn to coat on both sides. Cover and marinate in the refrigerator for 2 hours or overnight. Remove from the refrigerator 30 minutes before grilling. Heat the grill to high heat. Remove the steak from the marinade and season with salt and pepper to taste. Grill for 3 to 4 minutes on each side for rare to medium-rare doneness. Let rest 10 minutes before slicing across.
Toasted Garlic and Parsley Sauce:
Heat 1 tablespoon of olive oil in a small saute pan over medium heat. Add the sliced garlic and saute until lightly golden brown. Remove with a slotted spoon to a paper towel-lined plate. Heat 2 tablespoons of olive oil in a medium saucepan. Add the shallot, remaining chopped garlic, carrots and celery and cook until softened. Add wine and reduce by half. Add chicken and veal stock and cook until reduced by half. Strain the mixture into a clean medium saucepan. Add the toasted garlic, parsley, peppers and onion and cook for 5 minutes. Season with salt and pepper and spoon over the steak.
Goat Cheese Potato Puree:
Place goat cheese in a small food processor with 1/4 cup of the heavy cream and process until smooth. Rice potatoes into a large bowl. Mix in the butter and 1 cup of the heavy cream. Fold in the goat cheese mixture and season with salt and pepper to taste.