Have you checked out the additives and salt in those M&S ready meals.
If you can cook something as time consuming as lasagne why can't you fry off a few ounces of smoked bacon, bung in some baby onions or an onion chopped, add 500g of cubed casserole steak, a generous glass of wine, bunch of herbs, mug of stock with half a stock cube, pinch of salt and pepper and bung it in the oven for two hours to cook slowly along with some baked potatoes.
OR
500g lamb neck fillet, four or five carrots, chopped onion, handful of rosemary, salt and pepper, mug of lamb stock topped with sliced spuds in the oven for 90mins with the lid on and take the lid off for 1/2 hour after that.
That way you know what goes in it, where the meat comes from and its quality.
OR
packet of chicken thighs browned, cup of chicken stock, juice of a lemon, chopped small onion, spoon of curry powder, salt and pepper, stir in half a pot of creme fraiche and emtpy in a bag of washed spinach - serve with boil in the bag rice if you have to.
My MIL doesn't cook - her husband dropped dead from furred up arteries. She still doesn't cook. If DH goes there for a long weekend of packet food and shop bought cake his blood sugar (type 2 diabetes) is going through the roof by the time he gets back.
Not cooking is fine if it includes fresh, good quality simple ingredients. It is not fine if it includes ready meals, shop bought cakes and puddings and processed food.