In a large skillet, heat the olive oil over medium heat. Add the diced onion and minced garlic, cooking them together until the onion becomes translucent and soft, which should take about 3-4 minutes.
Incorporate the ground beef into the skillet. Use a spatula to break it into crumbles as it cooks. Continue cooking until the meat is nicely browned and fully cooked, approximately 5-7 minutes. Drain any excess fat.
Mix in the diced bell peppers and sauté them for an additional 2-3 minutes, just until they begin to soften slightly.
Stir in the chopped spinach, undrained diced tomatoes, Worcestershire sauce, smoked paprika, oregano, and season with salt and pepper. Cook for another 2 minutes.
Grease a 9x13-inch baking dish well. Begin layering by placing half of the thinly sliced potatoes on the bottom of the dish. Spoon half of the beef and vegetable mixture over the potatoes.
Add another layer of the remaining sliced potatoes followed by the rest of the beef mixture.
Cover the baking dish tightly with aluminum foil and place it into the preheated oven. Bake for 30 minutes.
After 30 minutes, carefully remove the foil. Sprinkle the shredded cheddar cheese generously over the top of the casserole. Return the dish to the oven and bake uncovered for an additional 15 minutes.
Let the casserole rest for a few minutes before slicing into squares and serving.
Notes
For an appealing presentation, serve each portion on a plate and consider garnishing with fresh parsley or a dollop of sour cream.