Pre-heat oven to 190 c, 375 f or gas mark 5. Dry fry the onion with the bacon until soft. Place into a shallow oven proof dish. Beat the eggs with the seasoning and herbs. Drain the tuna well and flake. Add to the dish with the bacon and onion. Pour on the beaten egg and arrange tomato and mushroom on top. Bake for 30 minutes or until set and golden brown.