Prepare a grill, or preheat the oven to 500 degrees F.

Prepare 4 sheets of heavy-duty aluminum foil to measure about 12 by 15-inches. Fold in half crosswise to crease, then unfold. Divide the spinach among the 4 foil sheets, placing it in the center of the bottom half.

Lightly coat both sides of each chicken breast with oil, then season with the Italian seasoning, 1 teaspoon of the salt, and 1/2 teaspoon of the pepper. Place one chicken fillet in the center of each spinach portion.

In a medium bowl, combine the onions, tomatoes, olives, garlic, wine, basil, thyme, remaining 1/2 teaspoon of salt, and 1/4 teaspoon of pepper, and stir to combine. Pile the tomato mixture on top of each chicken breast, spreading to cover evenly and allow any liquid to puddle around the chicken. Top each portion with 1 ounce of cheese.

One at a time, fold the top of the foil over the chicken, and starting at the corner, fold the edges of foil over to tightly seal, each fold overlapping the previous one. Place on the grill, or if using the oven, place the packets on a baking sheet and bake until the packages puff and the chicken is cooked through, about 12 minutes.

Remove from the grill or oven, and cut the tops of the packets open with a small, sharp knife. Serve immediately either in the foil packets, or by removing the chicken, toppings and sauce to dinner plates.