Combine lamb, breadcrumbs, garlic, egg and spices in a large bowl and season to taste. Mix with your hands until well combined. Roll tablespoons of mixture into balls and set aside on a tray.
Preheat oven to 180C. Heat 30ml oil in a large frying pan over high heat. Add meatballs and cook in batches, turning until browned (4-5 minutes). Transfer to a baking dish.
Heat remaining olive oil in a separate frying pan over medium heat. Add onion and cook until soft (5-7 minutes). Add tomato and cook until tomato just softens (1-2 minutes). Pour over meatballs and roast until meatballs are cooked through (10-15 minutes).
For Lebanese rice, heat butter and oil in a large saucepan over low-medium heat. Add onion and cook until soft (5-6 minutes). Add pasta and stir until just beginning to brown, then add rice and 1 litre water, stir to combine, bring to the boil, then reduce heat to low, cover with a lid, and cook until liquid is absorbed (10-12 minutes). Season to taste. Scatter meatballs with coriander and serve immediately with the Lebanese rice.