The area near where I work has many Beijing homestyle restaurants, and I've developed a bit of a repertoire for dishes I'll hint that should be ordered when we go so that I can eat. Homestyle cooking (jiachangcai / 家常菜) is unsurprisingly easy to cook at home, but also a style quite favoured by little hole-in-the-wall restaurants, and even some of the bigger ones.
Our usual restaurant doesn't have any English, and I'm actually not sure of its name, though I know it fairly well as we go there all the time. As a result this isn't so much a restaurant recommendation, but more of a things I eat because they're often vegan recommendation.
Shredded sour and spicy potatoes (算拉土豆丝) can be very sour and a little spicy, or very spicy and a little sour. I prefer a little sour and very spicy. This is a very dry dish, sometimes served with onion, and it's easy to go too far sour and too far spicy, but it's one of my favourites.
Okay I know you're going to notice a pattern, but sour and spicy cabbage (算拉白菜) is also pretty tasty. There is a whole lot of variation with this dish in the way it's prepared, unlike the potatoes, which are always shredded / 丝, but the result is always a slightly saucy, slightly sour or tart cabbage dish that goes really well with any of the spicier dishes you might have ordered.
Down the back of most menus, hidden away underneath and behind many other things, you might find something that reads suspiciously like cantonese vegetables / 广东菜. What they mean is gailan, and you can get them lightly wok-fried in soy sauce or with garlic or, if you're not careful, oyster sauce. I usually ask for them fried with garlic.
Eggplant has been a really awesome experience for me in Beijing. Almost every restaurant will have some sort of eggplant speciality. My favourite is 地三鲜, literally 'three earth treasures', which is potato, eggplant and capsicum and it's so good. Pictured above is an eggplant, capsicum and tomato dish, because when I asked for 地三鲜 on Thursday they said they didn't have any, which given they then gave me this and a potato dish makes me wonder but whatever. The sauce is amazing, the eggplant just soaks it up and so does the potato and it's so delicious. Sometimes you need to check the eggplant dishes to make sure no animals were harmed in the making of them, but this one is usually okay.
You might notice the lack of tofu dishes! That's because there's no tofu dish I can guarantee you is vego, so it's best to make enquiries as you go. But I have a tofu dish recommendation post lined up for soon!