Combine the egg, half of the soup or sauce sauce, bread crumbs, onion and peppers/mushrooms, 1/2 teaspoon of oregano, salt and pepper. Add beef; mix well.
On a large piece of foil or cling wrap, pat meat mixture into a 14-in. x 8-in. rectangle. Sprinkle cheeses to within ½” of edges.
Roll up, jelly-roll style, starting with a short side and peeling foil away while rolling. Seal seam and ends. Transfer to a 9-in. x 5-in. x 3-in. loaf pan (or whatever pan you like to use for meatloaf). Bake in oven for approximately 40 minutes or until loaf reaches an internal temperature of 155F.
At this point, if needed, pour out grease into a heat proof container. This will not be needed if you use a low fat content beef. Pour remaining soup or sauce over the top of the loaf. Place back in oven rotating a half turn.
Bake until internal temperature reaches at least 165F. Remove from oven, tent with foil and let rest for approximately 5 minutes.