Preheat oven to 350°F. Combine sauce ingredients in small bowl. Remove and reserve 1/4 cup for basting. Brush roast with remaining sauce.
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 55 to 65 minutes for medium rare; 65 to 75 minutes for medium doneness, basting with reserved 1/4 cup sauce after 30 minutes.
Meanwhile, remove and finely chop Swiss chard stems and ribs. Thinly slice chard leaves. Heat oil in large skillet over medium heat until hot. Add onion and garlic; cook and stir 5 to 6 minutes or until onion turns golden brown, stirring occasionally. Add chard stems and leaves, in batches if necessary; cook and stir about 2 minutes or until leaves are wilted. Cover and cook about 7 minutes or until stems are tender. Season with salt and pepper, as desired. Set aside and keep warm.
Remove roast when meat thermometer registers 135°F for medium rare; 150°F for medium. Transfer roast to carving board; tent loosely with aluminum foil. Let stand 10 to 15 minutes. (Temperature will continue to rise about 10°F to reach 145°F for medium rare; 160°F for medium.)
Carve roast into slices; season with salt and pepper, as desired. Serve with Swiss chard.
Nutrition information per serving: 200 Calories; 99 kcal Calories from fat; 11 g Total Fat; 3.5 g Saturated Fat; 0 g Trans Fat; 0.6 g Polyunsaturated Fat; 5.8 g Monounsaturated Fat; 55 mg Cholesterol; 280 mg Sodium; 6 g Total Carbohydrate; 1 g Dietary Fiber; 19 g Protein; 4 mg Iron; 546.3 mg Potassium; 6.6 mg NE Niacin; 0.4 mg Vitamin B6; 1.9 mcg Vitamin B12; 7.3 mg Zinc; 24.8 mcg Selenium; 13.9 mg Choline;