Slice bread into thirds or halves. You want the bread to be big enough to pick up but not so big you need a fork to eat it.
Brush the tops of the bread slices with olive oil on both sides and broil for one to two minutes, flipping halfway through, until very lightly browned.
In a medium bowl, combine mayonnaise, Old Bay seasoning, green onions, chives, dill, Worcestershire sauce, orange juice, orange zest and lemon zest.
Gently fold in crab.
Remove toast from oven and top with a heaping tablespoon of crab mixture. Place a tomato slice on top and sprinkle with about a tablespoon of cheese..
Place toasts in broiler for two to three minutes or until cheese is melted and bubbly.