You could always ask your T to bring her own lunch, since you feel a lot of pressure to fix something appropriate. That would take all the pressure off and let you concentrate on therapy - no having to cook or play hostess. If that feels too awkward, lots of stores have pre-made deli trays...you could pick up one and a package of sandwich rolls and just fix your own sandwiches. Or, you could pick up a pre-made salad.

Honestly, if T were to come over to my house for lunch, I would feel so much pressure to fix something tasty and then play hostess that we would get nothing accomplished.