For the sauce, add olive oil, 1 turn of the pan, to a medium pot over medium heat. When oil is hot, melt butter into oil. When butter foams, add grated onion and garlic, and season with salt, pepper and cumin. Stir 1 minute, add bay, stock, tomatoes and the cinnamon stick. Bring to a bubble and simmer 20-30 minutes so the flavors combine. Remove bay and cinnamon, adjust salt and pepper.
Meanwhile, preheat oven to 400°F and bring stock to a simmer in a saucepot. Add rice and cover; cook to tender, 18 minutes. Season with salt and pepper, and fluff with a fork.
Arrange the zucchini shells in a casserole or baking dish and drizzle with oil. Season with salt and pepper and roast 10-12 minutes. Remove from oven.
While zucchini bakes, heat a skillet over medium-high heat with 2 tablespoons oil, 2 turns of the pan. Add beef and brown and crumble; add onion and garlic, and season with salt, pepper and cumin. Once brown, remove from heat, combine beef with rice and add grated tomato and the fresh herbs. Adjust salt and pepper to taste.
Fill the par-baked zucchini with meat and rice mixture and top with a little tomato sauce. Bake to set the filling and sauce, about 20 minutes. Garnish with more chopped herbs, garlic-butter breadcrumbs and a little grated Parm or crumbled feta, if you prefer.