I have had significant periods of being alone (and DD hating my food so really cooking for 1).
I do a batch of various freezer meals on occasion, and enjoy 1 portion fresh and freeze maybe 4 more for other nights. Things like lasagna, spag bol, various curries, chilli con carne, cottage pie etc. Mostly they either need just reheating the sauce while some rice/pasta/potatoes cook, or throw it in the oven and ignore for 30 minutes or so.
If I am in the mood for stir-frying type meals, I will usually do a LOT of peeling/chopping of various veg, enough for 2 nights, and cook 1 lot but put the second lot in the fridge for following day to just toss and fry up. But possibly do 1 using diced chicken and the 2nd using fresh prawns, probably using 2 different sauces (whether from packets or just throwing bits and pieces into the pan like Chinese rice wine and soy sauce, or thai red curry paste/fish sauce/small tin coconut milk etc) and sometimes varying between different types of rice or noodles.
I will do a "cheat's roast" sometimes. I like doing diced potatoes that I season with garlic granules, pepper and olive oil, and throw into the oven. I also like to do roasted mediteranean veggies (I dice a load of peppers, courgette, red onion, mushrooms, tomatoes etc to the same size, add whole cloves of garlic, season with olive oil/balsamic vinegar/salt/pepper/herbs like basil/oregano/rosemary) as they are a great side dish and can be generally ignored as they roast, but leftovers can be served on pasta or frozen for another night.
And for meat - sometimes I would still do a small chicken and strip the carcass for other meals. But often I would just use a part boned breast or a couple of oyster thighs on their own. Sometimes plain, sometimes with lots of lemon, sometimes with some feta and thyme leaves under the skin, etc.
Decent sized lamb chops also roast nicely, or a lamb shank.
Very occasionally, I will do a full sized roast (if I am feeling energetic or will be busy later in the week so leftovers are useful or there's a good deal on) - enjoy a nice dinner that night, do lots of leftover things over a few days or sometimes even freeze leftovers for another time altogether. Gravy can reheat well, throw meat into that to reheat while you boil potatoes and fresh veg. Or very thinly slice before freezing and use in chinese type stirfries (these are great to use as various mixed meats from freezer, not just a single type).
Leftover chicken is the most versatile - risotto, soup, in a wine sauce with mushrooms, with various chinese sauces, or curries, in pasta with a tomato sauce, Spanish omlette for dinner and leftovers for next day's lunch etc.
But sometimes a slice of rare roast beef or lamb fried up on the pan with a dippy fried egg and some chips is devine. (Both are relatively versatile for other leftover meals). Pork is great for chinese type meals.
Bacon I would often use with cheese sauce, lots of veggies and pasta - and leftovers can be frozen and reheated as a pasta bake another time.
M&S sell various forms of "rarebit" (cheese in a teracotta pot) that needs heating in the oven - I cook a couple of part-baked bread rolls at the same time, and throw some sliced spring onions over the top if I am feeling fancy.