Red, White and Blueberry Turkey Burger

Ingredients

• 1 Tbsp. olive oil
• 4 shallots, thinly sliced
• 2 tsp. red wine vinegar
• 1 pound 99% lean ground turkey
• 6 oz. (about 1 cup) blueberries, smaller berries are better
• 3 Tbsp. plain whole wheat breadcrumbs
• 2 tsp. lemon juice
• 1 tsp. Dijon mustard
• 1 clove (1 tsp.) garlic, minced
• 1/4 tsp. kosher salt
• 1/8 tsp. black pepper, ground
• buttery cooking spray
• 2 oz. gruyere cheese, coarsely grated
• 4 whole wheat hamburger buns
• spinach leaves
• 4 tomato slices