Preheat your air fryer to 375°F (190°C).
Cut the chicken breast into even 1-inch strips and slice the bell pepper into thin strips.
In a large bowl, toss the chicken, broccoli florets, and bell peppers with avocado oil, garlic powder, onion powder, sea salt, and black pepper until evenly coated.
Place the chicken and vegetable mixture into the air fryer basket in a single layer, working in batches if necessary to avoid overcrowding.
Air fry for 12-15 minutes, shaking the basket halfway through, until the chicken is cooked through and the vegetables are tender with charred edges.
While the chicken cooks, whisk together the lemon juice and Dijon mustard in a small bowl to create the dressing.
In a separate serving bowl, combine the mixed greens and sliced cucumber, then drizzle with the lemon-dijon dressing.
Plate the warm air-fried chicken and roasted vegetables alongside the fresh garden salad and enjoy immediately.