Preheat oven to 350°.
Combine spinach and cream cheese. Press spinach mixture into bottom of a 13 x 9-inch baking dish coated with cooking spray.
Place breadcrumbs in a shallow dish. Cut each chicken breast in half horizontally to make 2 cutlets. Dredge chicken in breadcrumbs.
Heat oil in a large nonstick skillet coated with cooking spray over medium-high heat. Add chicken; cook 2 minutes on each side or until lightly browned. Arrange chicken over spinach mixture. Top with mozzarella, and sprinkle with oregano. Top with the tomato slices and Parmesan. Bake at 350° for 30 minutes. Spoon one-fourth spinach mixture onto each of 4 plates; arrange 2 chicken cutlets and 2 tomato slices over spinach mixture.
Note: Before making cutlets (see the third paragraph), partially freeze chicken for easier slicing.