Cook ravioli in microwave according to package directions.
While ravioli cooks, heat oil in a large nonstick skillet over medium-high heat. Add mushrooms, and onions; saute 3-4 minutes or until richly browned. Combine flour and next 5 ingredients in a small bowl, stirring until smooth. Add to pan, stirring well. Cook over medium-low heat a 2 minutes or until mixture thickens slightly.
Divide cooked ravioli evenly amount 4 shallow bowls or plates; spoon mushroom mixture evenly over ravioli. Sprinkle cheese evenly over each serving; garnish with basil, if desired.