Heat the oil in a large skillet and add the garlic. Add the lobsters, split side down, and cook, stirring, until the shells turn red. Cover and cook for ten minutes longer.
Cool the lobsters, remove the meat from the shells, and discard the shells. Cut the lobster meat into bite-size pieces. Discard the oil in the skillet.
Heat the butter in a skillet and add the mushrooms, pimiento, tarragon, olives, shallots, salt, pepper to taste, and lobster meat. Mix thoroughly and cook for five minutes. Add the sherry and the diablo sauce. Heat through and serve immediately.