Quarter apple and pear lengthwise and cut into each quarter on an angle to remove the core. Slice apple and pear into 1/4-inch thick slices. Squeeze a little lemon juice over the fruit to slow browning.
Cut the top rind off the brie and place in the microwave on high for 60 seconds. Depending on the ripeness of the cheese, it will take 60 to 90 seconds on high to heat and melt. If brie is not yet soft and hot after 1 minute, place it back in microwave for another 30 seconds on high.
Serve the softened, warm brie with a platter of fruit and Melba toasts for dipping and spreading. Reheat brie if it tightens up for 20 to 30 seconds at a time on high.