Preheat your oven to 350°F and prepare a baking sheet with nonstick cooking spray.
Season the chicken breasts with salt, pepper, and garlic powder.
Bake the chicken on the prepared baking sheet for 25 to 30 minutes, until the chicken reaches an internal temperature of 165°F.
Allow the chicken to cool slightly before cutting it into thin strips.
While the chicken cools, prepare the dressing. Blend all the dressing ingredients in a food processor until fully combined.
To build the salad, place the romaine lettuce and arugula into a large mixing bowl.
Top with the remaining salad ingredients and the sliced chicken and toss.
Add the dressing just before serving and toss to combine.