Prepare the Tribeca Oven Café Classic Garlic Loaf according to package instructions. Preheat oven to 400°F.
Pound the chicken to about ½-inch thickness. Pat dry chicken breasts. Marinate chicken in extra virgin olive oil, salt, black pepper, and garlic powder.
Grill chicken breasts about 7 minutes each side, rotating halfway for grill marks, or until internal temperature reaches165°F. Shred chicken when cooled.
In a sauté pan over medium heat, cook spinach in olive oil until wilted. Set aside.
Slice the Tribeca Oven Café Classic Garlic Loaf in half vertically, then in half lengthwise.
Spread butter onto the slices.
With the butter side down, place feta, sliced gouda cheese, spinach, and shredded chicken on the slice of bread. Place the other slice of bread with the butter side up.
Grill sandwich while pressed, until golden brown.