Place ginger in a food processor; process until it forms a paste. Remove and set aside. Repeat with garlic; remove and set aside.
In a small saucepan, heat 1 teaspoon oil over medium heat. Add rice and 1 teaspoon ginger paste; cook and stir until rice is lightly browned, 3-4 minutes. Stir in water; bring to a boil. Reduce heat; simmer, covered, until rice is tender, 15-20 minutes.
Meanwhile, for sauce, in a Dutch oven, heat remaining 1 tablespoon oil over medium heat. Add half the garlic paste and half the remaining ginger paste. Cook and stir until fragrant, about 1 minute. Add half the green onions and 1 tablespoon garam masala; cook and stir 1 minute longer. Stir in tomatoes, cream and 1/2 teaspoon salt; heat through (do not allow to boil).
For meatballs, preheat oven to 375°. In a large bowl, combine half the cilantro, the pepper and the remaining green onions, ginger and garlic pastes, 1-1/2 teaspoons garam masala and 1 teaspoon salt. Add chicken; mix lightly but thoroughly. Shape mixture into 1-1/2-in. balls. Place meatballs on a greased rack in a 15x10x1-in. baking pan. Bake until browned, 15-20 minutes. Transfer meatballs to sauce; cook until heated through. Stir in remaining cilantro.
For topping, combine sour cream, lime juice, cumin and salt. Fluff rice with a fork; serve with meatballs and sauce. Drizzle with topping; top with additional cilantro and green onions if desired.