Summer trip to Provence
Rather than complicating your day trip, I'd settle for lunch in Orange itself. Admittedly there are no remarkable restaurants in the immediate neighbourhood but there are enough good ones for a decent meal without having to interrupt or curtail your sightseeing. Le Forum, Le Parvis, Restaurant du Théâtre, Au Petit Patio. Rom'antique are all pretty good bets. Nothing amazing or surprising and all are definitely in the touristy category but, I think, convenience and practicality must sometimes short-circuit the search for the exceptional. Google each of them and see if one or other appeals. BTW, the Roman ruins (but since many are still in use, "ruins" is maybe the wrong word) and the late Renaissance/ baroque stuff will need 4 or 5 hours to do so don't count on a quick in-n-out tourist circuit. Not many Americans but lots of French and German tourists.
But you can have have some rather special meals within a 20-minute driving radius. For a splurge, the Chateau de Rochegute in Rochegute... but this comes with an AYOR label... the setting is superb but the food is very inconsistent ... I had a a great if overpriced meal there (in the summer) but on another occasion my parents experienced great disappointment (in the autumn). If you have wine-y tendencies, the Oustalet à Gigondas is run by the younger sons of a (sorta) well-known wine-producing family... prices are, however, more parisien than provincial but the level of cooking is first-rate and they do have a few "formules" that soften the blow ... the roasted veal sticks in my memory... although I never tried the dégustation, the folks at the surrounding tables seemed delighted by it. The caveau and restaurant Côteaux et Fourchettes stuck in the middle of nowhere at the Courançonne roundabout just outside Cairanne is where the local farmers/ vintners and the more clued-in Parisiens with residences secondaires in the area congregate.
If it's Saturday, I'd also take in the very sweet market in Sainte Cécile les Vignes.