Position a rack in the upper third of the oven and preheat to 500 degrees . In a large bowl, combine the tomatoes, garlic, EVOO, brown sugar, crushed red pepper and salt. Spread onto a foil-lined baking sheet and roast until the liquid has evaporated and the tomatoes are slightly charred, about 25 minutes. Transfer the tomatoes to a bowl and stir in the tapenade.
Spread the tomato jam over 8 bread slices. Layer each with roast beef, watercress and a non-jammy bread slice.