In a 1- to 1 1/2-quart pan over high heat, boil orange juice until reduced to 1/4 cup, 4 to 5 minutes. Let cool. Add shallots, lime juice, lemon juice, and cumin. Whisk in salad oil. Add chilies, plus salt and pepper to taste.
Remove and discard husks from tomatillos; rinse and cut into quarters. In a bowl, mix tomatillos with olive oil. Cut bread into 1-inch-thick slices. Set tomatillo quarters and bread slices on a grill over a solid bed of hot coals or a gas grill on high heat and turn as needed until browned on all sides, 1 to 2 minutes total for bread, 5 to 7 minutes for tomatillos. Let cool, Cut bread into 1-inch cubes.
In a large bowl, mix tomatillos, bread, arugula, and dressing. With a vegetable peeler, shave about 1/2 cup (2 oz.) thin slices off Manchego cheese. Mix cheese and salt and pepper to taste into salad.