- In a large skillet over medium-high heat, cook beef, breaking apart pieces with a wooden spoon, until lightly browned, 5 to 6 minutes.
- Season with 1 1/2 teaspoons salt and 1/4 teaspoon pepper. Add sweet Vidalia onion and garlic; cook, stirring, until translucent, about 5 minutes. Add pureed tomatoes, sugar, vinegar, tomato paste, Worcestershire and 1 1/2 cups water.
- Reduce heat to medium-low; simmer until thickened, about 20 minutes. Add chopped spinach just before serving and divide evenly among the buns.