Classic Roast Beef with Brown Gravy

WHAT YOU'LL NEED

• 1 Tbsp. olive oil
• 2 medium onions, chopped
• 4 lbs. beef eye round roast
• 1/2 tsp. salt
• 1/2 tsp. ground black pepper
• 3 cloves garlic
• 1 package Knorr ® Gravy Classics ™ Classic Brown Gravy Mix
• 1 1/2 cups water
• 1 Tbsp. balsamic vinegar
• 1 Tbsp. I Can't Believe It's Not Butter!® Spread