Thoroughly wash leeks, and chop all vegetables.
Saute vegetables in 1 tablespoon each, olive oil and butter, until wilted.
Remove from heat and set aside.
Slice potatoes and put into a bowl with cold water until ready to use.
Soften cream cheese for about 20 seconds in the microwave and stir in sour cream and cream.
Mix into vegetable mixture thoroughly.
Spray non-stick cooking spray onto casserole dish and layer potatoes, vegetable/sauce mixture and cheese, ending with cheese.
Sprinkle dried oregano on top.
Bake, covered, for 40-50 minutes, until hot and bubbly and potatoes are tender when pierced with fork.
Finish by placing the casserole under the broiler to brown the top.
