Begin by preparing your Seville oranges. With a sharp knife, carefully slice off the top and bottom of each orange. Stand the orange on one end and slice downward to remove the peel and pith, following the curve of the fruit. Cut the oranges into 1/4-inch thick rounds and set aside.
Slice the avocados in half, remove the pits, and peel the skin away. Cut the avocados into similar 1/4-inch thick slices.
Peel the red onion and slice it as thinly as possible, using a mandoline if available for consistent thickness.
In a small bowl, whisk together the extra-virgin olive oil, red wine vinegar, honey, sea salt, and freshly ground black pepper to create the dressing.
Arrange the orange and avocado slices on a serving platter, alternating them for visual appeal. Scatter the thinly sliced red onions over the top.
Drizzle the dressing evenly over the salad, ensuring each slice gets a taste of the vinaigrette.
Garnish with chopped fresh parsley and toasted almond slices, if using, for an added crunch and flavor.
Serve immediately or cover and refrigerate for up to an hour to allow flavors to meld.