In a medium bowl, stir together the tomatoes, peppers, avocado, cilantro, lemon juice, and salt. Cover and refrigerate.
In another medium bowl, stir together the oil, lemon juice, onion powder, garlic powder, chili powder, salt, and pepper. Add the chicken, making sure to cover each piece in the mixture, and let marinate for 15 minutes.
In a large pan over medium heat, add the chicken and cook for 5-6 minutes per side, depending on thickness, until golden brown and internal temperature is at 165°F.
Let the chicken sit for 5 minutes, the top with the salsa and serve.