How to Make It
Using a sharp knife, peel the red grapefruits, removing all of the bitter white pith. Working over a cutting board, cut in between the membranes to release the sections. Cut the grapefruit sections into bite-size pieces.
Squeeze the grapefruit membranes over a small bowl and reserve 1/4 cup of the grapefruit juice. Whisk in the tamarind concentrate, fresh lime juice, sugar, fish sauce and cumin. Whisk in the canola oil in a thin stream. Season the salad dressing with salt and Tabasco.
Transfer the grapefruit pieces to a large bowl. Add the avocados, onion, hearts of palm, cilantro and dressing. Toss gently and serve right away.