My grocery had no swordfish to be found. Do you think tuna steaks would be a good alternative?

Sure, why not? After all, you're just mixing some fish into beans and vegetables (in this case asparagus but it really could be any veg).

You could swap out the fish with meat (chicken, pork, beef, whatever).

Or you could even eat it vegan without the addition of fish. Or use tofu.

With dishes like this one, it's really up to you to pick something that will please those who will be joining you at your dinner table.