Season the chicken: Rub chicken breasts with olive oil, salt, pepper, garlic powder, and paprika.
Grill the chicken: Heat a grill pan or outdoor grill over medium heat. Cook chicken for 5–7 minutes per side until fully cooked.
Rest and slice: Remove chicken from heat and let it rest for 5 minutes. Slice into strips.
Prepare the salad base: In a large bowl, add mixed greens, cherry tomatoes, cucumber, and red onion.
Add avocado and chicken: Top the salad with sliced avocado and grilled chicken.
Make the dressing: Whisk together olive oil, lemon juice, mustard (if using), salt, and pepper.
Assemble and serve: Drizzle dressing over the salad and toss lightly before serving.