Combine 2 cups spinach, the feta and 3 tablespoons water in a bowl. Insert a paring knife into the thickest part of each chicken breast, cutting along the side to make a deep 2-inch-wide pocket. Stuff the spinach mixture into the pockets.
Heat a large nonstick skillet over medium heat and add the olive oil. Season the chicken with salt and pepper. Add to the skillet, rounded-side down, and cook until browned, about 3 minutes per side. Add the chicken broth, vinegar and sun-dried tomatoes. Partially cover and cook until the chicken is just cooked through, about 15 minutes.
Meanwhile, bring a pot of salted water to a boil. Add the ditalini and cook as the label directs. Put the remaining 1 1/2 cups spinach in a colander; drain the ditalini over the spinach to wilt it. Return to the pot.
Remove the chicken to a cutting board and slice. Add the pan sauce to the ditalini along with the mint and 1/4 teaspoon salt; toss. Serve with the chicken.
Photograph by Christopher Testani
Courtesy of Food Network Magazine