Heat oven to 350°F. Spread mustard evenly over all surfaces of beef roast. Press 1 cup crouton crumbs evenly onto roast over mustard.
Place roast, fat side up, on rack in shallow roasting pan. Insert ovenproof meat thermometer so tip is centered in thickest part of beef, not resting in fat. Do not add water or cover. Roast in 350°F oven 1-3/4 to 2 hours for medium rare; 2 to 2-1/4 hours for medium doneness.
Meanwhile toss green beans with oil on metal baking sheet. Add remaining 1/4 cup crouton crumbs; toss to coat. Roast in 350°F oven with beef roast 30 minutes.
Remove roast when meat thermometer registers 135°F for medium rare; 150°F for medium. Increase oven temperature to 450°F; continue roasting green beans 10 to 20 minutes or until tender and starting to brown.
Transfer roast to carving board; tent loosely with aluminum foil. Let stand 15 to 20 minutes. (Temperature will continue to rise about 10°-15°F to reach 145°F for medium rare; 160°F for medium.)
Carve roast into slices. Season beef and green beans with salt and pepper, as desired.
Nutrition information per serving: 463 Calories; 171 kcal Calories from fat; 19 g Total Fat; 5 g Saturated Fat; 7 g Monounsaturated Fat; 129 mg Cholesterol; 783 mg Sodium; 15 g Total Carbohydrate; 0.5 g Dietary Fiber; 54 g Protein; 4.8 mg Iron; 15 mg Niacin; 1.1 mg Vitamin B6; 2.8 mcg Vitamin B12; 9.6 mg Zinc; 60.3 mcg Selenium;