In a medium bowl, whisk together olive oil, lemon juice, Dijon mustard, red wine vinegar, sugar, shallots, oregano, parsley, salt, and pepper. The dressing should look smooth and well combined. Divide the dressing into two equal portions so one can be used for marinating the chicken.
Place the chicken breasts into a bowl or zip-top bag with half of the dressing mixture. Let the chicken marinate for at least one hour in the refrigerator for maximum flavor. I noticed the chicken becomes much juicier and more tender after proper marination.
Preheat your grill or grill pan over medium-high heat. Remove the chicken from the marinade and grill each side for about 5–6 minutes until fully cooked and golden brown. Allow the chicken to rest for a few minutes before slicing to keep the juices inside.
While the chicken cools, chop the romaine lettuce and prepare all vegetables and toppings. Slice the tomatoes, cucumber, avocado, and onions evenly for a beautiful presentation. Crisp bacon and fresh vegetables create the perfect mix of textures.
Place the lettuce into a large serving bowl and drizzle a little reserved dressing over it. Arrange the grilled chicken slices, tomatoes, corn, cucumber, bacon, onion, avocado, and blue cheese neatly on top. This step makes the salad look colorful and restaurant-style.
Drizzle the remaining dressing evenly over the salad right before serving. Toss gently if you prefer every bite coated with dressing. Serve immediately while the chicken is still slightly warm for the best flavor combination.