Heat oven to 450°. Place beef in ungreased shallow baking pan. Brush with 1 tablespoon oil; sprinkle all sides with salt, pepper and rosemary. Insert meat thermometer so tip is in thickest part of beef. Bake uncovered 20 to 25 minutes or until thermometer reads at least 140°. Cover beef with aluminum foil and let stand 10 to 15 minutes until thermometer reads 145°.
While beef is baking, mix pesto and mayonnaise in small bowl.
Reduce oven temperature to 400°. Brush bread slices with 3 tablespoons oil. Place in ungreased jelly roll pan, 15 1/2x10 1/2x1 inch. Bake 6 to 8 minutes or until crisp.
Meanwhile, cut beef into thin slices. Top each bread slice with beef and 1 teaspoon pesto mayonnaise. Garnish with basil leaf. Arrange appetizers on serving platter.