Here's what you need:
Here's what you need to do:
Mix first 4 ingredients and 1 1/2 tablespoons oil in medium bowl; mix in lamb. Shape into four 3/4-inch-thick patties. Cook patties in large nonstick skillet over medium-high heat 4 minutes per side for medium.
Meanwhile, preheat broiler. Broil buns until golden, about 2 minutes. Top each bun bottom with burger. Toss spinach, feta, onion, vinegar, and 11/2 tablespoons oil in bowl. Place salad atop burgers. Cover with bun tops, pressing firmly to compact.