There's quite a selection of restaurants and cafes in Heathrow T5
https://www.heathrow.com/at-the-airport/restaurants-a-z?&type=restaurant&terminalArea=5
Pret/Costa/Nero/Starbucks for quick coffee and sandwiches
Itsu for takeaway sushi
carluccios restaurant for Pizza and pasta
Girraffe restaurant for a mix of food (burgers, pasta etc)
and some other pub/bar options