Combine the ground beef, breadcrumbs, Parmesan, egg, minced garlic, parsley, kosher salt, and black pepper in a bowl. Mix gently just until the ingredients come together, then shape the mixture into approximately 18–20 small meatballs about 1 1/2 inches wide.

Heat the olive oil in a large Dutch oven or deep, wide skillet over medium-high heat. Brown the meatballs in a single layer for about 5–7 minutes, turning occasionally; transfer them briefly to a plate if the pan is crowded, and remember they do not need to be fully cooked yet.

Add the chopped onion to the same pot and cook for 3–4 minutes, until softened. Stir in the minced garlic and cook for about 30 seconds, just until fragrant.

Pour in the crushed tomatoes and water or broth, then stir in the kosher salt and optional Italian seasoning or oregano. Return the meatballs to the pot and add the spaghetti, pressing the strands gently into the liquid as they soften.

Bring the pot to a simmer, cover it partially, and cook for 15–18 minutes. Stir and separate the spaghetti every few minutes so it does not stick, and continue cooking until the pasta is tender and the meatballs reach an internal temperature of 160°F (71°C).

Taste the sauce and adjust the seasoning as needed. Let the finished pasta stand for 3–5 minutes so the sauce can thicken, then garnish with fresh basil or parsley and additional grated Parmesan.