For the beef: In a large pan with straight sides on medium-high heat, add the bacon and cook, while stirring, until crisp. Remove the bacon with a slotted spoon to a paper towel-lined plate. Leave the bacon fat in the pan and add the olive oil, beef, onion powder, garlic powder, oregano, salt and pepper. Brown the beef while breaking it up into bits, about 10 minutes. Remove the beef with a slotted spoon to a plate and reserve. Leave the fat in the pan for the sauce.
For the sauce: Add the butter and flour to the already-hot pan from the beef. If the butter begins to brown, lower the heat while working it into the flour. Cook, stirring, for a few minutes, then raise the heat and slowly whisk in the milk. Once it begins to thicken slightly, add the heavy cream and continue to cook until the sauce reduces a bit more and thickens as well. Add the mustard. The sauce will not be thick like gravy, but not as thin as water either. Taste and season with a pinch of salt.
For the casserole: Preheat the oven to 350 degrees F.
Using a 13-by-9-inch casserole dish, layer starting at the bottom with: a few spoonfuls of sauce to cover the bottom, half of the ravioli in 1 layer, the Swiss cheese, half of the beef, half of the tomatoes, half of the remaining sauce, the remaining ravioli in 1 layer, the American cheese, the remaining beef, the remaining tomatoes, the remaining sauce and the reserved bacon. Top with all of the shredded cheese blend. Bake until the edges are bubbly and the cheese begins to brown, 30 to 35 minutes.
Toss the lettuce and onion in a large bowl with the pickle juice. Serve each portion of casserole with a mound of this garnish over the top.