Steam the veggies, or in the case of the pumkin/sweet potato, boil or roast (which ever takes your fancy)
Make a white sauce...

60g butter melted in a pot, at 1/2 cup of flour, stir til you get a thick paste...
Add milk slowly til you get it fairly runny
Add in all your boiled/steamed/roasted veg, Stir in and break up (i hid veggies this way)
add a tin of Tuna/Salmon

Serve over pasta or rice or potato

Not sure how this goes with non dairy milk, but should be ok