Process first 8 ingredients in a food processor or blender 2 minutes or until smooth, stopping once to scrape down sides; set pesto mixture aside.
Butterfly roast by making a lengthwise cut down center of 1 flat side, cutting to within 1/2" of other side. From bottom of cut, slice horizontally to 1/2" from left side; repeat procedure to right side. Open roast, and place between 2 sheets of heavy-duty plastic wrap; flatten to 1/2" thickness, using a mallet or rolling pin.
Spread about two-thirds pesto mixture over roast. Roll up roast, jellyroll fashion, starting with long side, and secure at 2" intervals, using heavy string.
Place roast in a shallow roasting pan; cover with remaining pesto mixture. Bake, uncovered, at 450° for 15 minutes. Reduce heat to 350°; bake 1 hour or until a meat thermometer inserted into thickest portion registers 160°. Remove from pan, reserving drippings in pan; keep roast warm.
Whisk flour into drippings in pan, and cook over medium-high heat 2 minutes, stirring constantly. Add broth and next 3 ingredients; simmer 3 minutes or until thickened. Pour gravy through a wire-mesh strainer into a bowl, discarding solids. Stir in 1 teaspoon each parsley and thyme. Serve gravy with roast. Garnish platter, if desired.