Preheat the oven to 375 degrees F (190 degrees C).

Combine ground pork, ground beef, oats, milk, egg, salt, garlic powder, and pepper in a large bowl. Shape into 24 meatballs, about 1 1/2 inches in diameter.

Heat oil in a large skillet over medium heat. Cook meatballs until evenly browned, about 8 to 10 minutes. Place meatballs into an 8x8-inch casserole dish and scatter onion over top.

Combine maple syrup, mustard, ketchup, hot pepper sauce, and salt for sauce in a medium bowl. Pour over meatballs and toss to coat.

Bake in the preheated oven until set and cooked through, about 30 minutes, stirring halfway through.