In a mixing bowl, whisk together the Dijon mustard, 3 teaspoons of olive oil, and 1 teaspoon of finely chopped thyme leaves. Season with a pinch of salt and pepper to taste.
Add the chicken thighs to the marinade, ensuring each piece is thoroughly coated. Let it sit for at least 30 minutes to allow the flavors to meld. For best results, marinate in the refrigerator for a few hours.
Preheat your oven to 400°F (200°C). This temperature will ensure a perfectly crispy crust on the chicken.
In a separate bowl, combine the grated pecorino cheese and Gruyere cheese. Mix well and set aside.
Once the chicken has marinated, remove it from the bowl and shake off any excess marinade. Place the chicken on the prepared baking sheet. Spoon the cheese mixture generously over each chicken thigh, pressing down slightly to adhere.
Bake in the preheated oven for about 25-30 minutes, or until the chicken is cooked through and the cheese is golden and bubbly.
While the chicken is baking, prepare your salad. In a large bowl, toss together the mixed baby greens and halved cherry tomatoes. Drizzle with 1 tablespoon of olive oil and season with salt and pepper. Toss to combine.
Once the chicken is done baking, remove it from the oven and let it rest for a few minutes. Serve the pecorino crusted chicken on a plate alongside a generous helping of the mixed baby greens salad.
