Whisk dressing ingredients in medium bowl until creamy. Cut beef tenderloin tips into 1 x 1/2-inch pieces.
Heat oil in large nonstick skillet over medium-high heat until hot. Add 1/2 of beef; stir-fry 2 to 3 minutes or until outside surface of beef is no longer pink. Remove. Repeat with remaining beef. Season with salt and pepper.
Toss greens with 1/2 cup dressing in large bowl; place on platter. Top with beef and croutons. Serve with remaining dressing.