Not tomato sauce as in ketchup on your chips, but tomato sauce as in bung it on pasta sauce. Last night I sautéed a very little bit of onion and two chopped mushrooms (value ones, of course!!!) in a little bit of butter, added the sauce (which I've frozen in single portions) and some chopped chicken from the Sunday roast plus a little bit of balsamic vinegar, cooked 50g of pasta mixed the two and added 10g grated cheddar (6p per 10g) and it made the most scrummy dinner! As I liked it, I'm sharing.
Here's the tomato sauce recipe, both for Thermione and done the normal way. I wanted a fairly smooth sauce but you could leave the veg more chunky if you wished.