Unwrap pizza dough; do not unroll dough. Cut roll of dough into 4 even slices. Place dough, cut side down, on a baking sheet coated with cooking spray. Press dough with fingertips into 5-inch circles. Bake at 425° for 7 minutes. Remove crusts from oven.
Top crusts evenly with tomato slices and onion. Top each crust with 3 asparagus spears and 2 tablespoons cheese. Bake at 425° for 10 minutes or until crust is lightly browned and cheese is melted.
Combine salad greens and vinaigrette in a medium bowl, and toss gently to coat. To serve, place 1 cup greens on each of 4 serving plates. Place each pizzette next to bed of greens.