It's certainly not a hearty protein but I really like these little peppers, in the US I've only ever seen them sold as "Peppadew" but that apparently a brand name and they're technically called Juanita peppers.

They're pickled and sweet and tangy and really good on a veggie sandwich with hummus or avocado or the like to give a creamy savory flavor.

I originally became aware of them as "the weird sweet tangy peppers on the Mediterranean veggie sandwich at Panera" and spent a couple of years trying to figure out what they were called.

I actually just now found out that Peppadew was a brand and not a pepper variety.

Anyone used seitan or other more heartier vegan protiens in sandwiches?

No because I dislike sammiches but Future Lettuce's quick seitan has a tender, Chinese-style chicken texture that would go well in a sando:

https://files.catbox.moe/mxh23c.mp4

For a more complicated method that produces a ham-like luncheon "meat", I'd go for this recipe.

One filling for sammies or wraps that I think is pretty great is a veggie roast: get a tray, slap chunks of pumpkin, tomato, onion, garlic, and any other root vegetable or things like eggplant and capsicum and roast it all together with a coating of olive oil. Use as the base for a filling and add some herbs and leafy greens or other toppings like olives or capers as per your preference.

You can freeze this filling if you make a big batch of it ahead of time too.

A good slaw or kim chi will make anything shine. If you want a good veggie protein, refried beans for a torta or a bean dip can be used as a sandwich spread.

Falafel, avocado, cucumber, hummus. So good. The only vegan sandwich I ever really eat.

Pan seared large portabello mushrooms are great on sandwiches as the central ingredient, highly recommend.

I use fried tofu, I refry it with shredded ginger and say sauce, then the usual fixings lettuce tomato avocado spicy dill pickles and red onion. The red onion is the secret thats so yummy

If you don't mind a little spillage, lightly mashed refried beans or (fried) chickpeas go hard in my sandwiches and are proteiny. Or just mash them all the way into bean/chickpea burger for extra togetherness.

I guess not really veggie but I fuckin love peanut butter and banana sandwiches. I have to imagine that translates well to peanut butter and any veggie that goes well with peanut butter which is most of them.

Really liking the suggestions from others in the thread so I'll just add:

Having pesto with the sundried tomatos is pretty good as a starting point to layer on other flavours. I'm guessing you'd use nutritional yeast instead of parmesan for the saltiness in the pesto.

Also, if you don't mind staining the occasional white t-shirt, tinned beetroot is a great last-second addition to sandwiches if you think it's lacking character. I find it has a nice mellow sweetness that contrasts well against traditional savoury/sour pairings, without being too sweet like a chutney or relish.

Steamed eggplant slices tossed with some spiced oil, cherry tomatoes and basil. I've had it as a taco, but as a sandwich it should work, too.

Use miso paste as a spread, too!

A wild mushrooms salad is really nice. The salad has preserved mushrooms, onions and mayo in it, can use vegan mayo.

Pickled onions, mushrooms, cumumbers and other pickles are good too.

I really like a tomato, basil & mozzarella sandwich, but this isn't vegan.

Bell peppers on a sandwich are also really good raw, they have such a good crunch. I often have sliced bell pepper with some fresh cheese product, ricotta or such.

A paste with sun dried tomatoes and olive oil is very good.

Vegan cheese is also pretty easy to make so I sometimes use that.

Then I make this vegan lax from carrots that is amazing on a sandwich. It's all flavour and very easy to make. You pickle a carrot that has been thinly sliced lenghtwise in salt, liquid smoke, sugar and spices of choice overnight.

There's this local tofu dip that I like to make egg salad sandwiches with. Found lots of different recipes online but this one sounds about right: https://www.copymethat.com/r/LzkYtQwyy/homemade-tobys-tofu-pate/

Anyone used seitan or other more heartier vegan protiens in sandwiches?

Hell yeah. It's not very hard to make a good log out of vital wheat gluten, and if you slice it thin it can be a good substitute for roast beef or ham.

Also bbq soy curls on a burger bun are kinda like a bbq chicken sandwich.