2 egg omelette with mushrooms or cheese and a jacket potato
Asda:
eggs, 16.7p each (cheapest available, £1 for 6)
mushrooms, 10p for 2-3 (50p for 250g)
cheese, 19p for a 30g portion (£1.65 for 250g)
Baking potatoes, 11p (four for 45p)
Total per portion, 54p for the mushroom option or 63p for the cheese. Disclaimer: it costs around 14p in electricity so cook jacket potatoes in an oven for around 45-60 minutes.
Pasta with tomato sauce and grated cheese.
Basic range pasta, 5p for an 80g portion (32p for 500g)
Chopped tomatoes, 9p for quarter of a tin (38p a tin)
cheese, 19p for a 30g portion (£1.65 for 250g)
Total per portion, 32p but that doesn't include cooking time and - frankly - plain chopped tomatoes, especially cheap tinned ones, with no salt/pepper, herbs, or garlic aren't particularly nice
Cauliflower cheese
Cauliflower, 22p for a quarter (88p for a whole one)
cheese, 19p for a 30g portion (£1.65 for 250g)
Milk, 17p for a quarter pint (69p a pint, 500ml needed for sauce)
Flour, 2p (55p for a 1.5kg smartprice bag, 50g needed)
Total, 60p but again nit including fuel costs.
Not a single suggestion these is less than 30p and that's before fuel, travel costs, etc. The per portion model also presumes you have enough money to buy the whole items needed to take a portion from and somewhere appropriate to store the unused amounts until needed again.