I want to cook Portuguese seafood stew without the seafood. Any suggestions?

Not sure what recipe you refer to, but, as you're proposing radical changes to ingredients, perhaps it would be best to determine what it is about the recipe that you do want to preserve and work up from there. Like similar fisherman's stews, Portuguese caldeiradas are general pretty open ended, the ingredients depending on locality and the day's catch.

There are those here who would (rightly) say that it's no longer Portuguese seafood stew if you omit (for whatever reason) the seafood.
That acknowldged, you could make a Portuguese-style stew going in a couple directions from the original....
1) some recipes use cod, clams & mussels. So you add more cod to make up for the absent clams & mussels.
2) some use seafood or fish stock; choose fish stock or (less flavor) water
3) some recipes use sausage. You could use all one or several types of sausage to make up the volume of missing seafood. But then we're getting far from Portuguese seafood stew and you might want to start with a recipe for Italian sausage stew, to get ingredients and seasoning in good proportions.
https://www.foodnetwork.com/recipes/braised-italian-sausage-stew-recipe-2119484