Preheat broiler. Arrange the bread slices on a baking sheet and broil them for 1-2 minutes on each side, until lightly golden and toasted.
In a medium bowl, combine crab meat, mayo, chopped onions, peppers, dill, salt and pepper. Squeeze a lemon wedge and mix well.
Spread the crab mixture evenly on toasts. Top each toast with two slices of tomato and top with gruyere first and parmesan last. Add a few dill leaves
Broil at 375°F for about 5-7 minutes until cheese melts and the top looks golden brown.