Verde Valley Fajitas

1 (1 1/2 to 2 pound) skirt steak or lean flank steak, or
    6 chicken breast halves, boned and skinned

Marinade
1/4 cup vegetable oil
2 tablespoons lemon juice
2 tablespoons soy sauce
2 tablespoons chopped scallions
1 clove garlic, minced
1 teaspoon coarsely-ground black pepper
1 teaspoon celery salt
1 teaspoon jalape