4 hoagie rolls
4 oz. provolone cheese, shredded
1/4 cup water
1 1/2 cups jarred marinara sauce
2 large eggs, lightly beaten
1 1/2 oz. Parmesan cheese, grated
1/3 cup minced onion
1/2 cup fine, dry breadcrumbs
1/2 pound spicy Italian turkey sausage, casings removed
1/2 pound ground turkey (with dark meat)
1/2 tsp. black pepper, divided
1/2 tsp. kosher salt, divided
1 1/2 tsp. minced garlic
1 tbsp. extra-virgin olive oil
1 package fresh baby spinach, divided