Personally I wouldn't bother with tinned. A small salmon fillet can be steamed in the microwave and added to some mashed potato. Or some fresh haddock or pollock, you can poach it in a bit of milk. Just put it in a shallow bowl, cover with milk, cover with clingfilm and microwave for a minute or so (check it's cooked through) You can run your fingers around it before it's cooked to check it's got no bones in.
I used to buy fish fillets and cut them in to teeny portions and freeze them so I just had to take one out, cook it as per above and add to any vegetables.
as you move away from purees on to little pasta shapes you could try making a tomato sauce which you can freeze in portions. You can then add a teeny bit of tinned tuna to it and hey presto, tuna pasta for tea