Jorge's Pasta-less Eggplant Lasagna

Soak eggplant slices in a large bowl of lightly salted water for 30 minutes. Drain and pat dry with paper towels. Cook and stir ground beef in a skillet over medium heat until browned, 5 to 7 minutes. Remove from heat. Preheat the oven's broiler and set the oven rack about 6 inches from the heat source. Whisk olive oil and Italian seasoning together in a bowl. Brush both sides of eggplant slices with the seasoned olive oil. Arrange eggplant slices on a baking sheet and place in preheated oven; broil until browned, 2 to 4 minutes on each side. Set oven to 400 degrees F (200 degrees C). Measure 1 cup of Parmesan cheese and set aside. Stir ricotta cheese, egg, and remaining Parmesan cheese together in a bowl. Stir spaghetti sauce, diced tomatoes, and ketchup together in a separate bowl. Spread a small amount of spaghetti sauce mixture in the bottom of a casserole dish. Top spaghetti sauce mixture with a layer of broiled eggplant slices. Cover eggplant layer with a layer of the ricotta mixture. Sprinkle a layer of feta on top of the ricotta mixture. Cover feta layer with ground beef layer. Sprinkle a layer of spinach on top of ground beef. Repeat with remaining ingredients, ending with a final layer of eggplant topped with the reserved 1 cup Parmesan cheese. Bake in the preheated oven until sauce is bubbling and cheese is browned, about 40 minutes. Let cool for 10 minutes before serving.