Vegan

Marinated fish is used to add fat, salt, umami, and a hint of acid, maybe some funkiness, in a soft, lightly chewy texture.

Salt, umami, and savory acid can come from the marinade itself: soy sauce, vinegar, maybe some lactic acid from fermented/pickled vegetables.

Not every component has to come from the same ingredient, and the beauty of a bowl is that you just need to hit all the notes across all the ingredients.

So something like smashed marinated cucumbers, seaweed salad, pickled radishes, vinegared sushi rice, sesame oil, sesame seeds, seaweed flakes, will already hit a lot of the major notes expected in a poke bowl. The satisfying chew of marinated cooked mushrooms, tofu or other processed soy or maybe even edamame, seitan, or whatever your preferred textured protein is (vegan cheese substitutes can sometimes work, test the flavors for complementing the Hawaiian/Japanese leaning ingredients in the bowl).

In the end, poke bowls are rice bowls. Mix some flavors that work together, like modern Hawaiian combinations (drawing on Japanese, Chinese, Korean influence). Or get ambitious mixing stuff from other cultures and flavors.