Lightly grease a deep dish 13 by 9" casserole dish. In a large saucepan over medium heat, melt the butter and saute' the garlic just until fragrant. Stir in the flour until it foams. Whisk in the milk and stir until mixture thickens into a white sauce. Mix in the chicken, oregano and pepper flakes and salt.
Spoon 1 to cups of white sauce into the casserole. Layer 4 noodles on top. Spread 1/2 of each cheese over the noodles. Spread all of the greens on top. Add another 1-2 cups sauce , 1/3 of noodles and the remaining cheese. Sprinkle the black olives evenly over the cheese.
Cover with foil and bake for 40 minutes. Uncover and continue baking until golden brown and bubbly, about 20 minutes. Garnish with tomatoes just before serving.