COOK rice following package directions, omitting salt, in a medium saucepan.
HEAT an extra-large frying pan over medium-high. Add oil, then onion. Cook until soft, 2 to 3 min. Crumble in beef and garlic. Cook, stirring occasionally, until no pink remains, 4 to 5 min. Stir in sugar, chili powder, cumin and salt, 1 min. Season with fresh pepper. Add 1 cup water and tomato paste. Boil, then reduce heat to medium-low. Simmer until saucy, about 10 min.
STIR sour cream with remaining 2 tbsp water and chili-garlic sauce in a small bowl. Divide rice among 4 bowls. Top with beef mixture, lettuce, tomatoes and avocado. Top with sour cream mixture.