As far as a larger meal at lunch, you could always try one of the buffets. Biergarten in Germany at Epcot is wonderful. We had dinner there last year and the food is delicious, and it would certainly be your larger meal of the day! You sit at tables of 8, so if your party consists of fewer than 8 people (or more than 8 people in which case you would sit at 2 tables), you will be sitting with people you do not know. DH and I love this, so it did not bother us at all but everyone is different.
People say good things about the Tusker House buffet at AK, and I believe they serve lunch too.
Crystal Palace at MK is a character buffet, but many adult-only groups enjoy going there. The food was certainly delicious last year at dinner, and I hear rave reviews as well for lunch. The characters are Winnie the Pooh, Tigger, Eeyore and Piglet. If the adults in your party like children, it is very cute when the characters have the napkin parade around the restaurant with some of the children dining there. Very cute to watch!
I hear very good things about 50s Prime Time at DHS, and it is inexpensive. We are considering this for a lunch as well on our July trip.
Whispering Canyon Cafe at Wilderness Lodge is supposed to be very fun, and they have an all-you-can-eat skillet option as well as an a la carte menu.
Any of the other restaurants in Epcot's World Showcase are good options too. Maybe the only one I would not recommend so much is the one in Norway, which is supposed to be good, but it is a princess meal and is more expensive than other character lunches, although I believe it also includes a photo package in the price.
For counter service, Cosmic Ray's at MK is very good, and they have larger meal options like chicken and ribs (I think it costs around $14). Tangierine Cafe in Morocco at Epcot is also excellent, we had lunch there. They have a really great shawarma platter with different side dishes, also about $14 I think. These CS places also have smaller options, such as a falafel at Tangierine Cafe or a burger or a sandwich at Cosmic Ray's. So even if some of you are not too hungry to eat a large meal you could find a smaller one at these locations.