Season chicken breasts with salt & pepper, cook 6–7 minutes per side until 165°F, rest 5 minutes, then slice.
In a bowl, whisk mustard and honey, add vinegar & garlic, slowly whisk in oil, season to taste.
In large bowl, add greens, tomatoes, cucumber, carrots, onion, avocado, and sliced chicken.
Drizzle dressing, toss gently, taste & adjust, serve immediately.