Heat the olive oil in an ovenproof skillet (cast iron is great) over high heat, add the scallions and garlic, and sauté for 1 minute. Add the asparagus. Cook for another minute, stirring gently. Add the tomatoes and basil. Pour in the eggs and tilt the pan so that they spread all over the surface. Reduce the heat to low and cook the frittata until the bottom is set, 8 - 12 minutes. Place the frittata under the broiler, and broil until the top is golden 5 - 7 minutes. Cut into wedges and serve, either hot or at room temperature.