Cook bacon in a 4-quart heavy pot over low heat until some of fat is rendered, about 5 minutes. Add onion, celery, and garlic and cook, stirring occasionally, until vegetables are softened but not browned, 7 to 8 minutes. Stir in spices. Add stock and tomato sauce and bring to a boil. Stir in cauliflower rice and simmer, uncovered, stirring occasionally, until some of liquid is absorbed and cauliflower is cooked through, about 5-7 minutes. Stir in butter, salt, and pepper to taste, then remove from heat and let stand 5 minutes.