Pat the chicken breast dry with paper towels. If very thick, butterfly or pound to an even 3/4-inch thickness. Season both sides with 1/2 tsp kosher salt and 3/4 tsp freshly ground black pepper.

Cook chicken

Heat 1 tablespoon olive oil and 1 tablespoon butter in a large skillet over medium-high heat until shimmering. Add the chicken and cook undisturbed 4–5 minutes until a golden crust forms. Flip and cook another 4–5 minutes until internal temperature reaches 165°F (74°C) or juices run clear. Remove chicken to a cutting board and let rest 5 minutes, then slice thinly against the grain.

Sautéed vegetables

Sauté mushrooms and aromatics

In the same skillet (add 1 tablespoon olive oil if pan is dry), add sliced mushrooms and spread in a single layer over medium-high heat. Let mushrooms brown, stirring occasionally, about 4–5 minutes. Add 1 teaspoon minced garlic and 1/2 teaspoon thyme, season with 1/4 tsp salt and 1/4 tsp pepper, then sauté 1–2 more minutes until garlic is fragrant and mushrooms are tender. Remove from heat and set aside.

Balsamic vinaigrette

Whisk dressing

In a small bowl or jar, combine 1.5 tablespoons balsamic vinegar, 3 tablespoons extra-virgin olive oil, 1/2 teaspoon Dijon mustard, 1/2 teaspoon honey, 1/4 teaspoon salt, and 1/4 teaspoon black pepper. Whisk or shake until emulsified. Taste and adjust sweetness or acidity as desired.

Salad assembly

Divide 4 cups mixed greens between two plates or one large serving bowl.

Evenly distribute halved cherry tomatoes (1 cup) and thinly sliced red onion (1/4 cup) over the greens.

Top greens with the warm sliced chicken and sautéed mushrooms, arranging slices so some crust is visible.

Sprinkle 1/2 cup crumbled bleu cheese over the salad and add 1/4 cup toasted nuts if using.

Drizzle the balsamic vinaigrette over the assembled salad (use about half initially, then add more to taste). Toss lightly or leave arranged and serve immediately so warm chicken and mushrooms contrast with cool greens.