Arrange bread in a single layer on a baking sheet. Broil 2 minutes on each side or until toasted.
Lower oven temperature to 300°.
Melt butter in a large nonstick skillet over medium heat. Add onion and next 4 ingredients (through garlic); cook 10 minutes or until onion is translucent, stirring frequently. Increase the heat to medium-high; sauté 4 minutes or until onion begins to brown. Add sugar; sauté 2 minutes. Stir in vinegar and Worcestershire; remove from heat. Add dates and cheese; stir until combined.
Top each toast with about 2 teaspoons onion mixture. Bake at 300° for 4 minutes or until cheese melts.