In a mixing bowl, combine the balsamic, 2 teaspoons of the salt, oregano, and crushed red pepper and whisk until salt is dissolved. Whisk in the garlic and olive oil. 

Place the chicken thighs in a resealable plastic food storage bag. Set 1/4 cup of the balsamic mixture aside, then add the remaining balsamic mixture to the bag with the chicken. Seal the bag and then turn it over several times so that the chicken is evenly coated. Set the chicken aside to marinate, either 45 minutes to an hour at room temperature or up to overnight, refrigerated. 

Preheat the oven to 425 degrees F. Line a 13- by 17-inch baking sheet with aluminum foil for easy cleanup. 

If the chicken has been refrigerated, let it come to room temperature, about 30 minutes, then place the thighs on the baking sheet, drizzling any marinade remaining in the bag over the chicken. Roast in the center of the oven for 30 minutes. 

While the chicken is roasting, combine the pepper strips, onion wedges, and tomatoes in a large bowl and drizzle with the remaining 1/4 cup balsamic marinade. Toss to coat well. Sason with 1/4 teaspoon kosher salt and toss again. 

When the chicken has cooked for 30 minutes, remove it from the oven and scoot the pieces to one side of the baking sheet. Place the peppers, onions, and tomatoes on the baking sheet, stirring to coat with any juices from the chicken, and return to the oven until the chicken is deeply golden and the veggies are caramelized around the edges, usually 15 to 20 minutes longer. 

Remove from the oven and garnish with the crumbled Feta cheese and oregano leaves. Serve hot with crusty bread. 

Serves 6