Heat oil and butter in a 12-inch skillet over medium-high heat. When butter has melted, add half of the asparagus to the skillet with tips pointed in one direction; add remaining spears with tips pointed in the opposite direction.
Using tongs, distribute spears in an even layer (spears will not quite fit into single layer). Cover skillet; cook until asparagus is bright green and still crisp, about 5 minutes.
Uncover, increase heat to high and season asparagus with salt and pepper to taste. Cook until spears are tender and well-browned along one side, 5 - 7 minutes, using tongs to occasionally move spears from the center of the pan to the edge of the pan to ensure all are browned.
Transfer to serving dish, adjust seasonings as needed and, if desired, squeeze lemon over spears. Serve immediately.