In a 13 X 9 baking dish, add oil, ketchup, soy sauce, vinegar, sugar, pepper, garlic and cumin then whisk well. Add London broil to mixture, then using a fork, poke many holes into roast and continue to roll on both sides until completely covered. Cover meat with plastic wrap and refrigerate at least 4 hours, but overnight is best. Be sure to turn occasionally to marinate both sides. Preheat grill on medium. Place water soaked mesquite chips under grill grate. Place meat on grill and sear both sides. Reduce grill heat and cook on medium low for 60-70 minutes total. Continue turning, keeping lid closed in between turns. Baste with extra marinade sauce while cooking until cooked to medium rare. Remove from grill and cover with foil then let stand 10 minutes. Using an electric knife, slice London broil very thin across the grain. Serve with favorite steakhouse potatoes.