Dice onion and mince garlic. Cut zucchini un half lengthwise then into 1/2-inch slices. Dice tomato. Set aside.
Heat olive oil in a 10-inch cast iron or other high-sided skillet over medium-high heat. Add ground beef, breaking up with a spoon, and cook until brown.
Add onion, garlic, and zucchini, and cook, stirring occasionally for 5 minutes. Add spices, salt, 1/4 cup water, and diced tomato. Cover and simmer for 10 minutes, to allow flavors to combine. Garnish with chopped tomato and serve directly from skillet.