1. Season the chicken with salt and pepper. Heat 2 tsp oil in a large nonstick skillet over medium high heat. Add the chicken to the pan and cook until the chicken is browned and cooked through, about 3 minutes per side. Transfer chicken to a plate.
2. Add the remaining 2 tsp oil to the pan, still over medium high heat. Add scallion whites, cooking and stirring for 1 minute. Add the garlic. Cook and stir 30 seconds more. Add the tomatoes and corn to the pan. Cook until softened, about 3 minutes. Stir in the scallion greens and season with salt and pepper to taste.
3. Place 1 c of vegetable mixture on each plate. Top with chicken breast and slices of avocado. Sprinkle with lime juice and serve.