Stuffed Breast of Chicken

Name: Stuffed Breast of Chicken
Ingredients: 1 tablespoon vegetable oil; 3 ounces spinach, stemmed, and washed (about 3 cups); 1 cup ricotta cheese; 1/4 cup grated Asiago; 1/2 teaspoon ground nutmeg; 1 teaspoon kosher salt; 1 teaspoon freshly ground black pepper; 6 chicken breasts, boneless, tenderloin attached (about 3 pounds); 1 cup unsalted butter, room temperature; 3 cloves garlic, minced; 1 tablespoon chopped fresh rosemary leaves; 1 tablespoon chopped fresh thyme leaves; 1 tablespoon chopped fresh marjoram leaves; Kosher salt and freshly ground black pepper