Preheat the oven to 350 degrees. Line a baking sheet with parchment paper and set aside.
In a saucepan over medium heat, add the 1 teaspoon olive oil and shallot. Allow to sautee for 3-5 minutes or until translucent. Add the spinach and stir, until the spinach has wilted down.
To a bowl, add the shallot spinach mixture, sun-dried tomatoes, feta, and mozzarella. Stir until the mixture appears uniform, and the feta is crumbled evenly. Set aside.
With a knife, create a pocket within the chicken breast, as if you were cutting a pocket in pita bread. Try to go near the edge without poking through. It does not need to be perfect.
Mix the chicken marinade ingredients together, then spread over the top and bottom of each breast. Place the chicken on the baking sheet, evenly spaced apart.
Scoop about ¼ cup of the stuffing mixture and spoon into the chicken breast pocket. If there is leftover stuffing, then evenly distribute among the chicken breasts until all the stuffing has been used.
Bake the chicken breasts for about 30-35 minutes, or until the internal chicken temperature reaches 165 degrees. Allow to rest for at least 5 minutes before slicing through. Enjoy!