Place bread cubes in a bowl; pour milk over bread. Let stand 5 minutes.
Gently combine soaked bread cubes, beef, cumin, coriander, pepper, 1/4 cup cilantro, and 1/8 teaspoon salt in a medium bowl. Gently shape into 12 (1 1/2-inch) meatballs.
Heat a Dutch oven over medium-high. Add oil to pan; swirl to coat. Add meatballs in a single layer; cook, turning to brown on all sides, about 4 minutes. Transfer meatballs to a plate. Add squash, onion, and garlic to pan; cook, stirring occasionally, 3 minutes. Add stock, scraping pan to loosen browned bits. Add remaining 1/2 teaspoon salt; cook until liquid is reduced by half, about 6 minutes. Add tomatoes and tomato sauce; bring to a simmer. Cook, stirring occasionally, until slightly thickened, 6 to 8 minutes. Stir in cauliflower; cover and cook 3 minutes. Return meatballs to pan; cover and cook just until meatballs are cooked through, 6 to 8 minutes. Sprinkle with remaining 1/4 cup cilantro.