Chicken Florentine Burgers

Name: Chicken Florentine Burgers
Ingredients: 1 1/2 cups white wine, preferably Pinot Grigio; 1/2 large sweet onion, finely diced; 3 medium cloves garlic, minced; 3/4 pound ground chicken breast; 3/4 pound ground chicken thighs; 1 1/2 teaspoons salt; 3/4 teaspoon freshly ground black pepper; 2 teaspoons Dijon mustard; 12 ounces frozen chopped spinach, thawed and squeezed dry of all liquid; 3 ounces grated Swiss cheese; 1/2 cup plain bread crumbs; Olive oil; 6 sourdough rolls, split horizontally; 6 slices Swiss cheese; 6 slices beefsteak tomato