Burgers with Spicy Avocado Sauce

INGREDIENTS

• 1 avocado, peeled and chopped
• 1/2 cup Hellmann's® or Best Foods® Real Mayonnaise
• 1/3 cup chopped fresh cilantro
• 3 Tbsp. cayenne pepper sauce
• 1/2 tsp. grated lime peel
• 1 Tbsp. lime juice
• 2 lbs. ground beef
• 1 medium onion, cut into 1/4-inch-thick slices
• 8 hamburger buns, split