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