Local Montreaux/Wengen/Lucern Restaurants

Wengen is pretty small and there are not a lot of 'hidden gems' as far as restaurants go. However, I always make sure to eat dinner at the family-run Hotel Bären (5 mins walk downhill from train station). They have a large terrace with great views, and a lot of their food is sourced from local suppliers (including veggies from their own garden). Fresh and creative, it's a step above the "touristy" cuisine you find in a lot of mountain towns.
Based on other posts, I see you are traveling with the family, so definitely book ahead for dinners if possible. The Swiss are big fans of making reservations.
Lucerne: There are tons of great restaurants so it's hard to narrow things down, but here are a few ideas - not necessarily "hole in the wall" type places but popular with local residents. Restaurant Weisses Schloss and Restaurant Helvetia (both near Helvetiaplatz in the 'new' town, a bit away from the tourist crowds) for seasonal classic Swiss food. The Taube restaurant (near the Jesuit church, next to the river) also serves hearty local food in a very nice atmosphere (in or outside).
If you are by the Lion Monument, stop at Alpineum cafe. Good lunches or just a place to sit down and take a break.
The Rathaus brewery right on the river has decent food and good beer - plenty of tourists but lots of locals too. Nice to sit outside there and people watch, or enjoy the vaulted ceilings inside. La Cucina is a nice Italian place that is classy but not stuffy, so ok for the younger family members. It's in a hotel, but doesn't feel touristy and it's popular with locals for lunch and dinner.
Other places include Mill'Feuille by the "other" wooden bridge (good all day, something for everyone, nice river view) and if you go up to the city walls, check out the Hofbeiz farm shop/restaurant behind - a unique "farm in the city" they do a nice farm breakfast on weekends and offer smaller snacks and dinner as well. Not open every day so just check beforehand.
If you've had enough Swiss/Italian food - Takrai is a great little Thai takeaway near the lake (and St Leodegar church) that is a local favorite. Huge portions and you can walk across the street to eat it lakeside.
And for a real, actual "hole in the wall" -- Twiny Station is a hugely popular sandwich takeaway in Old Town. The pouletschnitzel (chicken schnitzel) sandwich is the specialty. Nothing fancy, but if you just want to grab a baguette sandwich and sit by the lake, you can check it out and decide if the locals are onto something or not...I myself am not totally clear :)

One favourite of mine in Wengen is the hotel Berghaus. Nice terrace overlooking the village and the landscape, and, as a pleasant change from the usual Swiss fare this place specialised in Fish. But local fish, sourced from the lakes. Friendly place run by a local family that has been there for ages. Highly recommended.

I went out for dinner in Wengen last weekend (May 6) to the only restaurant that was open: Pasta & More. I wouldn't call it a hole-in-the-wall (that would have been a vending machine that night), but the food was excellent. My husband ordered pasta and I ordered a grilled chicken in a Swiss mushroom & asparagus sauce. Touristy perhaps (as is everything up there), but the food was satisfying.

Hotel Bären if known for their excellent quality in food. We took half-board when we stayed there, and dined there every night. Do make a reservation.

Like Nickelini, we also ended up at the pasta & more in wengen and we loved it!! My sister and I had the best chicken caesar salads. They were open when most places were closed between lunch and dinner.

At many of the train stations, including Lucerne, is the sandwich shop Brezelkönig. At the lucerne train station, it’s on the same level as the trains. I could eat their avocado sandwich every day. And I just might when I return next month. 😊