Heat oven to 425°F. Spread 1/4 cup pesto evenly onto all surfaces of beef Tri-Tip Roast; sprinkle with pepper.
Place roast on rack in shallow roasting pan. Do not add water or cover. Roast in 425°F oven 30 to 40 minutes for medium rare; 40 to 50 minutes for medium doneness.
Meanwhile combine tomatoes and onion in small saucepan. Cook over medium heat 15 to 20 minutes or until onion is tender and most of the liquid has evaporated. Stir in remaining 1/4 cup pesto. Keep warm.
Remove roast when instant-read thermometer registers 135°F for medium rare; 150°F for medium. Transfer roast to carving board; tent loosely with aluminum foil. Let stand 20-25 minutes. (Temperature will continue to rise about 10°F to reach 145°F for medium rare; 160°F for medium.)
Carve roast across the grain into thin slices. Season with salt and pepper, as desired. Serve with tomato sauce and sprinkle with cheese.
Nutrition information per serving: 297 Calories; 162 kcal Calories from fat; 18 g Total Fat; 5 g Saturated Fat; 4 g Monounsaturated Fat; 67 mg Cholesterol; 517 mg Sodium; 6 g Total Carbohydrate; 0.8 g Dietary Fiber; 26 g Protein; 1.9 mg Iron; 6.7 mg Niacin; 0.5 mg Vitamin B6; 1.3 mcg Vitamin B12; 4.3 mg Zinc; 27.6 mcg Selenium;