In a bowl, combine Boneless, Skinless Chicken Breast (16 ounce) that you've cut into 1-inch pieces, Worcestershire Sauce (2 tablespoon), and Corn Starch (3 tablespoon). Let marinate for 1-2 hours.
In a pan, heat Vegetable Oil (2 tablespoon). Add Frozen Spinach (1 cup), Onion (1), and Salt (1/2 teaspoon). Cover and let cook for 3-4 minutes over low-medium heat.
Stir, then cook for another 10 minutes, until onions are tender. Set aside.
To the cooled spinach and onion mixture, add Mayonnaise (1 cup), Black Olives (1/2 cup), and Sour Cream (1/4 cup). Mix well.
Preheat oven to 375 degrees F (190 degrees C).
In a pan, heat Oil (2 tablespoon). Add chicken and stir-fry over medium heat until browned. Set aside.
To assemble, spoon spinach mayo onto each Hoagie Roll (6). Add Tomato (1), chicken, another layer of spinach mayo, and Shredded Mozzarella Cheese (to taste). Transfer finished sandwiches to a baking sheet lined with nonstick baking paper.
Bake sandwiches for 5-6 minutes.