To make the meatballs, place in a large mixing bowl the ground beef, zucchini, onion, garlic, cilantro, salt, black pepper, cumin, oregano, chili powder, allspice, egg, and cracker crumbs. Either using your hands or a spoon, mix all the ingredients until well combined.
Preheat the oven to 375°F and lightly grease a large baking sheet or 2 large cast-iron skillets. Form the meat into tablespoon-sized meatballs and place on the sheet (you should get about 28). Bake the meatballs for 20 minutes or until lightly browned.
Meanwhile, in a blender mix together the tomatoes, chipotle chiles, onion, garlic, cumin, oregano, allspice, chicken broth, and lime juice. Blend until a smooth puree is formed. Adjust the seasonings and add salt to taste.
Pour the tomato-chipotle sauce into a large pot, but wait until the meatballs are done before turning on the heat. When the meatballs are done, bring the pot to a boil and then turn down the heat to a simmer. Add the meatballs to the pot and continue to simmer covered for 30 minutes.
Serve warm with bread or tortillas, garnished with cilantro and crumbled Cotija cheese.