2 teaspoons olive oil, plus more for the baking dish
1 medium onion, finely diced
2 garlic cloves, minced
2 pounds spinach, cleaned, trimmed, and coarsely chopped, or 2 10-ounce packages frozen chopped spinach, thawed and thoroughly drained
1/4 cup stock or water
1/2 cup milk
6 ounces reduced-fat cream cheese
Worcestershire sauce, to taste
Hot sauce, to taste
1 cup grated mozzarella
Kosher salt and freshly ground pepper
Baguette slices, breadsticks, or crackers, for serving