Beef, Blueberry & Flax Burgers

Ingredients

• 1 pound Ground Beef (93% or leaner)
• 1 cup fresh blueberries
• 2 tablespoons Dijon-style mustard
• 2 tablespoon balsamic vinegar
• 2-1/2 teaspoons minced garlic, divided
• 2 teaspoons Worcestershire sauce
• 1/3 cup ground flax seed or meal
• 1/2 teaspoon salt
• 1/2 teaspoon pepper
• 4 cups lightly packed mixed salad greens
• 2 ounces crumbled feta cheese