Preheat the oven to 375°F (190°C).
Heat olive oil in a large skillet over medium heat. Add the chopped onion and green bell pepper and sauté for 4-5 minutes until softened.
Add the minced garlic and cook for 1 minute until fragrant.
Add the ground beef to the skillet. Cook, breaking it apart with a spoon, until browned and cooked through, about 7-8 minutes.
Season the beef mixture with salt, black pepper, dried oregano, and dried thyme. Stir well to combine.
Sprinkle the all-purpose flour over the beef mixture and stir to coat evenly. Cook for 1-2 minutes to remove the raw flour taste.
Gradually pour in the beef broth while stirring continuously. Bring the mixture to a simmer and cook for 3-4 minutes until the sauce thickens.
Remove the skillet from heat and stir in the sour cream until fully incorporated.
In a greased 9×13 inch casserole dish, spread half of the thawed hashbrowns evenly on the bottom.
Pour the beef and sauce mixture evenly over the hashbrowns layer.
Top with the remaining hashbrowns, spreading them evenly.
Sprinkle the shredded cheddar cheese evenly over the top layer of hashbrowns.
Bake uncovered in the preheated oven for 30 minutes, or until the cheese is melted and bubbly and the casserole is heated through.
Remove from the oven and let rest for 5 minutes before serving.