1. Mix the oil, vinegar, garlic, salt and pepper together, and brush the mixture on the flank steak. Cover and refrigerate for 1 hour or overnight.
2. Meanwhile, heat the olive oil in a medium skillet over medium heat. Add the raw red pepper, shallot and garlic and season with salt and pepper. Cook until the peppers soften, about 5 minutes.
3. Add the roasted red peppers and vinegar and cook for 5 minutes more.
4. Remove from heat, cool and stir in the basil and pine nuts. (This can be stored in the refrigerator for up to 1 week. It should be served at room temperature.)
5. Preheat the grill to high heat.
6. Grill the flank steak for 4 to 8 minutes on each side, depending on the desired doneness. Let the steak rest on a carving plate for 1 or 2 minutes before slicing.
7. Slice the steak on the bias and serve it with the red pepper pesto.
Serving Size: about 1/4 pound steak with pesto