I've tried to work in fish as much as possible, but since fillets of the right fish are pricey, I often go to (a good) canned tuna to handle the job.
These have been really good and can be even better the next day. I usually make 4-5 large potatoes, but my wife and daughter just eat a half at a time due to the size.
Basically twice baked potatoes. It does not smell or taste fishy.

Tuna Taters
The full recipe:
Wash down the spuds, dry
Rub down with olive oil, cover in coarse sea salt.
--this is to dry out the skin, if salt conscious like I am, most of the salt comes off in the process or you can brush off when they come out of the oven
No wrapping in foil, no poking holes etc. This makes the skin really good to eat.
Put on a rack on a cookie sheet so heat can get all around. Flip about 30 min in.
Bake at 425° for an hour 10 min.

Cut in half, score each around in a circle to help in scooping out the the inside without breaking it. Scoop them out, put that in a bowl.
In the bowl, mix 3-4 5oz cans of a good tuna. I like Bumblebee solid in water. Costs a bit more, but a lot less than buying fillets and it's identifiable as actual fish. LOL
Fat free or low fat grated cheese of your choice, about 6oz or a small bag.
4 tbs olive oil
Season with garlic powder and course ground pepper
A couple of teaspoons of Liquid Smoke, or a few tbs of worcestershire.
Chives, fresh cut or dried
Might want a splash of almond milk or whatever you prefer if it seems too dry, but prob not necessary.

Mix it all up. It doesn't need to be the consistency of mashed potatoes, but close.
Fill the skins with the mixture, it will be piled high.
A little more of the cheese on top.

Bake again, 350­°, I usually let it go about 25 min to get hot all the way through again.
The next day I'll usually heat in the microwave, but give it a few minutes in the oven.
Don't burn yourself! The skin is the best part, eat the whole thing.

The stats: (with regular grated cheese IIRC, so it could be better with the fat free or low fat)

436 cal, entire potato, half for half obviously
Total Fat: 13.5g
--sat fat: 3.8g
Cholesterol: 54.2mg
Sodium: 329mg (if you wipe off the salt from the initial baking)
Carbs: 23g
--Fiber: 2.2g
--Sugars: 1.5g
Protein: 26.8g

Alternatively:
A couple of times I've added some thick sliced deli roast beef on each half. Kind of a steak and potatoes taste without springing for steak. Leave out some of the tuna for space.

As a much easier alternative, but less presentable:
Skip the scooping and mixing, just bake the potatoes as described. Good for prepping at the first of the week by just baking a whole mess of spuds. I usually make a couple extra when doing the full recipe above, just for me to eat later in the week. When time to eat, throw it all in the bowl at once, cut it up, mix and heat it up. Makes for a good lunch without any real time involved.