Cut oranges, lime and lemon in half and place flesh side down on a parchment lined pan. Roast the citrus fruit in a 350 degree oven for 1 hour or until the fruit caramelizes. Remove and let cool.
To make the dressing, squeeze ¼ cup juice from cooled citrus in a small bowl. Add balsamic vinegar, gourmet mustard, salt and pepper to taste. Add olive oil and whisk together until well blended. Taste and adjust seasoning as needed.
Layer the spinach, Romaine lettuce, red onion, cucumbers, tomatoes and avocado on a serving platter. Drizzle citrus dressing over the salad and serve extra dressing on the side./p>