Toast the bread to your desired level of doneness.
While the bread is toasting, cut the top and bottom of the grapefruit off. Then cut off the rind all the way around until you have the pink grapefruit flesh exposed. Carefully use your knife and cut the segments out of the grapefruit by cutting on each side of the white membranes that separate the segments.
When the toast is ready, smash half of an avocado over each slice of bread. Top with segments of the grapefruit.
Drizzle with balsamic glaze or a dash of balsamic vinegar. Top with chopped pistachios and a sprinkle of salt. Serve immediately.