In a gallon-size resealable bag, add the chicken, then season with the salt, pepper and onion powder. Add the minced garlic, red onion, bell pepper and zucchini. Pour the salad dressing into the bag, seal, and shake together, making sure everything is well coated. Refrigerate for at least an hour to marinate.
1-1 ½ pounds boneless, skinless chicken (thighs or breasts), cut into 1 inch pieces, 2 teaspoons kosher salt, ½ teaspoon black pepper, ½ teaspoon onion powder, 3 cloves garlic, minced, 1 red onion, cut into 1-inch pieces, 1 yellow bell pepper, cut into 1-inch pieces, 1 large zucchini, cut into ¼-inch slices, ½ cup Italian salad dressing