Greek Lamb Burgers with Spinach and Red Onion Salad

INGREDIENTS

• 1 1/2 cups baby spinach leaves
• 2 teaspoons paprika
• 1/3 cup chopped fresh mint
• 1/2 teaspoon salt
• 1 1/2 teaspoons balsamic vinegar
• 4 1/4-inch-thick red onion slices
• 1 1/3 pounds ground lamb
• 1 1/3 cups crumbled feta cheese
• 4 hamburger buns or small ciabatta rolls
• 3/4 teaspoon ground cinnamon
• 3 tablespoons olive oil, divided