Ok this is how I make mine, it's not really complicated, just lots of options very much based on what I have...
Chop onion and garlic, fry gently in large saucepan with oil until soft. Add a little chilli if you like (fresh/dry/whatever). Add diced carrots or celery if using. Fry gently a bit more. Scoop most of the veg out when soft to make room.
Turn up heat a little bit, chuck in peppers and/or mushrooms/bacon if using. Fry off. Scoop out.
Put in splash more oil and mince, fry until just beginning to brown. Chuck all veg back in. Add tinned tomatoes/passata/fresh toms/whatever. Mug of boiling water with stock cube. Or stock. Or just boiling water. Splash of red wine if you have any lying around. Add lentils if you're sneaking them in (you won't taste them!).
For depth of flavour add in any of these you have: splash of Lea&Perrins or teaspoon of marmite/bovril, squirt of tomato puree and/or tomato ketchup. Tsp of dried herbs (Italian/Basil/Majoram). Give a good stir, put lid on, leave to simmer on low heat for as long, poking it occassionally to stop sticking.
When reduced serve with pasta.
Next day, add more tomatoes, tinned/cooked kidney beans, maybe tinned/frozen sweetcorn, Either add some tabasco/dried chilli to the main sauce, or if you can be bothered fry up another onion with some chilli, plus cayenne/coriander/paprika/if you have them. then add to sauce, warm through for as long as you can. Serve with rice/jacket pots.