My favourite recipe book has basic cooking time for chicken pieces as:
160 (non fan - I use 150 fan) for 45 minutes, then baste, then another 25 minutes. All uncovered.
I have learnt this formula.
Then I use different marinades, some to a proper recipe and others just winging it. My basic premise is that all marinades must have some kind of acid (lemon/vinegar), at least a small amount of fat (usually olive oil but you could use sesame oil eg if doing a more Asian style), spices/herbs. Alcohol is optional and something to sweeten it slightly (honey, tomatoes, cinnamon) is useful. Plus regular seasoning.
Eg, I might do something using tomato sauce, olive oil, sherry vinegar then add five spice and paprika for a simple version, or a more complex version with lemon juice, olive oil, brandy/whisky (smokiness/sweetness), honey, garlic, oregano, and cumin.
Or soy sauce, honey, sesame oil, lime juice, chilli, ginger, garlic.
Options clearly endless. My dad is all about the basics - thyme, oil, lemon and garlic.
I do salmon fillets cooked in oven in foil "pouches" with soy sauce, ginger and lime juice and then about 1tablespoon of water in each package. Cook for 17 minutes at 170 fan. Serve with rice/noodles and steamed veg and use the liquid from the parcels as a sauce.
If frying meat, a pat of butter and some lemon juice and salt into the pan while the meat is resting makes a quick cheat "sauce".
Roasted vegetables in large dishes involve almost zero faffing and can be eaten as is with pasta/couscous (maybe some feta/goats cheese) or can be whizzed up into a paste. I add cream cheese/quark/creme fraiche for extra creaminess, or extra olive oil if too thick (include tomatoes as one of the roasted veg). A friend adds walnuts. Works as a "pesto" on pasta or as a thick sauce over chicken/meat. I froze this in portions when I was doing no-carb at night as I would defrost a portion for me.
Tahini, lemon juice and greek yoghurt makes a great "dressing" to be dribbled over veg to make them more interesting - just experiment with amounts and add water/olive oil if necessary to get the right consistency. Sprinkle some sesame seeds to make it look better (or nigella seeds work as well). Fancier versions can be looked up online but I usually start with roughly similar amounts of each then adapt.