How do I make tasty seitan in a pressure cooker?
In my experience a pressure cooker does not greatly influence the taste nor the texture of seitan.
The same recipes apply for cooking in a regular soup pot and in a pressure cooker, but here are some suggestions that might help:
Texture:
The sponginess can be reduced by making a bit dryer (less hydrated) seitan dough and kneading it a little more, which makes it more compact and chewier.
Also I find that the next day (after the cooked seitan was sitting in broth) the texture tends to be a bit better.
Flavor:
If the broth is too weak (cause of diffusion) the flavor gets washed out of the seitan ... so I always make quite a strong broth (i.e. on the spacier/saltier side). Adding something like some shiitake can help add more richness and umami.

I had great success with variants on this Miyoko's recipe for &quot;unturkey&quot; ... at least the proportions/ratios of spices/salt/soysauce are quite good ... but then you can experiment with different spices (I like it with a bit of smokiness and heat, so I usually add some chipotle chiles).
What this recipe also suggests is:

adding a little bit of chickpea flour to the active gluten (1/4 cup chickpea to 4 cups of gluten), and
pre-baking the seitan before boiling

both also contribute to a nicer texture and crust.