Make the vinaigrette. In a mini-food processor, add the sun-dried tomatoes, oil, orange juice, vinegar, shallot, salt and pepper. Process until smooth. Marinate the chicken in the vinaigrette for 30 minutes. In a large skillet over medium heat, add oil and sauté the onion until soft and translucent, about 10 minutes. Add the garlic and continue to sauté until onions are caramelized, about 5 more minutes. Spoon the mixture into a bowl and set aside. In the same skillet, add the butter and cook the chicken thighs, searing to a deep golden brown. Add the finely diced sundried tomatoes, 4 cups of chopped spinach, feta, mozzarella, sautéed onion and garlic. Sprinkle with salt and pepper and stir to combine. Lower the heat, cover and cook until the chicken reads 165 degrees on a meat thermometer. Remove the chicken to a cutting board. When cool enough to handle, dice or rough chop the thighs. In a large bowl, add 2 cups of spinach, the chopped romaine, dates or figs, and the cooled chicken. Scrape and spoon out the drippings from the skillet and toss into the salad. Add more salt, pepper and olive oil as needed. Serves 6-8.