Preheat the oven to 375°F (190°C).
Heat olive oil in a large skillet over medium heat. Add diced onion and minced garlic, sauté for 3-4 minutes until softened.
Add ground beef to the skillet. Cook, breaking it apart with a spoon, until browned and cooked through, about 6-8 minutes. Drain excess fat.
In a large mixing bowl, combine the cooked ground beef and onions, frozen Potatoes O’Brien, cream of mushroom soup, sour cream, milk, salt, black pepper, and smoked paprika. Mix well to combine.
Transfer the mixture into a greased 9×13-inch baking dish and spread evenly.
Sprinkle shredded cheddar and mozzarella cheeses evenly over the top.
Cover the baking dish with aluminum foil and bake for 30 minutes.
Remove the foil and bake uncovered for an additional 15 minutes, or until the cheese is melted and bubbly and the potatoes are tender.
Remove from oven and let the casserole rest for 5 minutes before serving.