Pat dry chicken breast cubes and season with garlic powder, salt, and pepper.
In a large pan, heat up oil and add the chicken pieces. Cook, stirring throughout, for about 7 to 9 minutes, until the chicken pieces are done and have reached an internal temperature of 165F. Turn off the heat, and remove the chicken from the pan onto a plate.
In a large bowl, place tomatoes, cucumber, red onion, cooked chicken pieces, chopped basil, and croutons. Sprinkle feta cheese over the top. Pour vinaigrette and toss to combine. Serve immediately.