I've actually found a reasonable fast food place in the Eaton Centre -- A Taste of Satay is in the north food court on the bottom floor near Dundas. If you order the rice, meat and vegetables for $4.29, it isn't greasy. (If you order the chicken balls, it's at your own risk!) The menu is pretty limited though, so I've been taking the opportunity to nip over to old Chinatown for quick lunches.
The place I've most frequented is Garden Restaurant. This is your "duck hanging in the window" place, and it's fast. There may be a lineup for seating if you arrive between 12:05 and 12:35, but otherwise, single people share a table of 4 to 6, and get their own pot of tea. It doesn't take much time for them to assemble a bit of meat (BBQ pork, steamed chicken, etc.) with a few fronds of bok choy and rice or noodles. It's quick and probably the best choice for a quick lunch near the Eaton Centre.
I was there a few days ago, and, looking for something different, noticed a spicy beef soup at the bottom of the lunch menu. The waiter said that it would take a few minutes longer, because it's done in the back kitchen rather than at the front window, but it didn't take that long. The soup was a rich broth with a few specks of chili floating in it -- and the skins from two whole chilis were in the bowl. The noodles were the thick chewy kind that is served in the north of China. (It reminded me of the soup I had once in a famous but downscale restaurant in Beijing, near the Kempinski). I'm okay with spicy, and the soup was spicy enough that I didn't want to drain the broth all the way to the bottom, to deal with the chili residue.
The other choice in the area is Yueh Tung, on the second floor on the corner (entrance off Elizabeth Street). The menu here is more varied -- I met a friend who is vegetarian for lunch, so a wider selection is better. The restaurant is larger and nicer, and a plate of food probably runs in the $5.50-$6.00 range (as opposed to the $4.50-$5.00 range at Garden Restaurant).
In the grand scheme of things, it's been a luxury for me to bounce back and forth between the restaurants for lunch. They're so cheap, and the quality is good. We're lucky to have these choices in Toronto (and I haven't even gone over to the New Treasure or Chinese Palace places for dim sum, on the north side of Dundas).
[I'm saying this as I'm about to head off for three weeks in Europe, so I'm trying to maximize my consumption of Chinese food before I go ....]