Do you really need an alternative? Can't just simple vegan/vegetarian lasagna or what ever be without meat substitute?
Some people put soy pieces, actually I don't like it because it really can be to much meat alike. The same as vegan sausages.
Tofu, seitan, Tempeh, chickpeas, beans…
Jackfruit is super cool as well. If it is super ripe and raw it gives sweetish kind of pineapple flavor. I like it. If it is from a can usually it is perfect for the meat like dishes. And the seeds you can toast and it tastes like chestnuts.
Some time ago I wrote it and there is a recipe with jackfruit, well it is kind of a mix of things found at home Jackfruit