Ingredients:

• (1 lb.) ground bison
• (1/2 cup) cooked spinach, squeezed dry
• (1/2 cup) crumbled feta cheese
• (2 tsp.) fresh dill, chopped
• (1 tsp.) fresh oregano, chopped
• (1 tsp.) ground cumin
• (1 tsp.) minced garlic
• (3/4 tsp.) kosher salt
• (1/2 tsp.) freshly ground pepper
• (3/4 cup) nonfat or low-fat Greek-style plain yogurt
• (1 tsp.) freshly grated lemon zest
• (2 tsp.) lemon juice
• (1 tsp.) fresh dill, chopped
• (1 tsp.) fresh mint, chopped
• Pinch of kosher salt
• Freshly ground pepper, to taste
• (4) French rolls (or 4 in. pieces of whole-wheat baguette), split and toasted
• (16 thin slices) English cucumber
• (8 slices) vine-ripened tomato
• (4 thin round slices) red onion