1. Heat oven to 450 degrees F. Rub beef with oil. Season with garlic salt; press peppercorns onto top and sides of beef. Place on rack in roasting pan.
2. Roast in 450 degrees F oven 40 minutes (130 degrees F to 135 degrees F on instant-read thermometer). Remove beef from pan; let stand 10 minutes (temperature will rise to 145 degrees F for medium-rare).Sauce:
3. With cooking spray, coat nonstick skillet. Add shallot, garlic; cook over medium, stirring, 5 minutes. Add thyme, oregano, salt, 1-1/4 cups broth. Reduce to 1/2 cup, 10 minutes.
4. Strain sauce; return to skillet. In small cup, mix 1/4 cup broth and flour. Stir into sauce in skillet; boil 1 minute to thicken. If sauce is too thick, stir in another 1/4 cup broth. Keep warm.Potatoes:
5. In saucepan, combine potatoes, 1 teaspoon salt and enough water to cover. Cook, covered, over medium heat until tender, 30 minutes.
6. Meanwhile, in small saucepan, mix broth, spread, shallot, remaining 1/2 teaspoon salt, pepper and nutmeg. Bring to boiling. Remove from heat.
7. Drain potatoes; return to pan. Add broth-yogurt spread mixture; mash to desired consistency. Stir in parsley. Serve beef with sauce and potatoes.