Preheat oven to 450°F. Line a baking sheet with aluminum foil. Place baguette rounds on baking sheet and set aside.
Heat 1 Tbsp. of olive oil in a large pot over medium-high heat. Add garlic and onion to pot and cook, stirring frequently, until onion is softened and fragrant, 3-4 minutes. Pour in tomatoes, salt and meatballs. Bring to a boil, cover, and turn heat to low. Cook, stirring occasionally, until meatballs are warmed through, approximately 15-20 minutes. Remove pot from heat, stir in basil, and let sit 10-15 minutes until meatballs are cool enough to handle.
While meatballs are cooling, brush baguette slices with remaining olive oil. Bake in preheated oven 4-5 minutes until toasted. Remove pan from heat and set aside.
Once meatballs have cooled slightly, remove from pot with slotted spoon and place on cutting board. Slice each meatball in half.
Spoon a generous amount of tomato mixture onto each baguette round, and top with half a meatball. Cover meatball with a sprinkle of mozzarella and Parmesan, and finish with a dusting of oregano. Repeat until all bruschetta have been assembled.
Place baking sheet in oven and cook 5-6 minutes, until cheese is melted and golden. Remove from heat and let sit 2-3 minutes before serving. Makes 30.