Preheat 375 degrees F. To a small baking dish, add the beet, olive oil, balsamic vinegar, one teaspoon of salt and zest from the naval orange. Fill up the baking dish with water so the beet is submerged in water. Cover the dish with foil and transfer it to the oven to braise for 1 hour, or until the beet is tender when poked with a fork. Remove from the oven; using tongs, transfer the beet to a cutting board to cool. When it's cool enough to handle, shave the beet's skin. Cut the beet into a small dice. Depending on how big your beet is, you may only need about 1/2 of the beet for this salad.
To prepare the citrus fruits, start by slicing off about 1/4-inch off the stem end. Slice off the other end and rest the citrus on its now-flat surface. Take your knife and slice off the pith and peel in a vertical motion. Ultimately you want the citrus to be pith-free. If there are any bits of white pith, take your knife and carefully slice it off. Repeat with the remaining citrus fruits. Slice the blood orange and navel orange into 1/4-inch thick rounds. Transfer the rounds of citrus to a plate and arrange how you like. NOTE: In the pictures above, you'll notice that I segmented the grapefruit. You can do this too, or you can simply slice the grapefruit into rounds. I did it because the pomelo was simply too big for the plate.
Transfer the watercress to a bowl and pour in about 1 teaspoon or two of olive oil and a pinch of salt. Rub the leaves, making sure they're evenly coated. Place the mound of watercress in the center of the plate. Garnish the salad with the reserved cubed beet, diced avocado, mint and Italian parsley. Drizzle the citrus with a bit of olive oil and top with a sprinkling of salt.