For meatballs:

Line large rimmed baking sheet with plastic wrap. Char chiles over direct flame or in broiler until blackened on all sides. Enclose in paper bag and steam 10 minutes. Stem, seed, and peel chiles, then chop finely (should yield about 3/4 cup).

Place chiles in large bowl. Gently mix in beef and all remaining ingredients. Using moistened hands and scant tablespoonful for each, roll meat mixture into 1-inch meatballs. Arrange meatballs on sheet.

For soup:

Heat oil in large pot over medium heat. Add onion with any juices and garlic. Sauté until onion is tender, about 3 minutes. Add chile powder and cumin; stir 1 minute. Add broth and oregano; bring to rolling boil. Reduce heat to very low, just below bare simmer, and cook 10 minutes.

Stir zucchini and rice into broth. Increase heat to medium and drop in meatballs, 1 at a time. Return soup to simmer. Cover and cook gently until meatballs and rice are cooked through, stirring occasionally and adjusting heat to avoid boiling, about 20 minutes. Add 1/4 cup cilantro and 1 tablespoon lime juice. Season soup with salt and add more lime juice by teaspoonfuls, if desired.

For toppings:

Heat 3 tablespoons oil in heavy medium skillet over medium heat 1 minute. Add half of tortilla strips. Cook until crisp, gently separating strips with tongs, 2 to 3 minutes. Transfer strips to paper towels to drain. Repeat with remaining tortilla strips, adding more oil if needed.

Ladle soup and meatballs into bowls. Top with tortilla strips and cilantro.

* Often called pasillas; available at some supermarkets and at specialty foods stores, farmers’ markets, and Latin markets.

** Available in the Asian foods section of some supermarkets and at Asian markets.

*** Available in the spice section of many supermarkets and at Latin markets.