Also refried beans greens and queso Fresca with a little pico makes for a great taco.
I also find offal meat tacos to be more filling than muscle cuts and usually they come as street tacos much smaller even forgoing the cheeses. I believe nose to tail is an important part of sustainable meat use and it seems in much ive read that the organs often are more nutrient dense. Maybe that's why they seem more filling.
Cutting sausage with oats makes goetta! Its a Cincinnati area treat that really crisps up nice!
I've noticed that in sauces the addition of mushrooms onions tomatoes squashes and even greens will help to make it more filling and also satisfy the texture that my western pallete longs for.
I haven't found a way to make a small burger more filling yet but I'm sure there are many ways... topping with hearty mushrooms or just swapping out the patty for a big portobello top often hits the spot.