I think the reality is that if you are on a very strict calorie controlled diet, there's a fairly high chance your food will be less interesting and satisfying. That's just a fact unfortunately.
Having said that, @bellac11 , lemon juice, greek-style yoghurt and fresh herbs/spices make surprisingly good, and low calorie, dressings for salads and vegetables.
Also, I reiterate the air fryer advice. I still use oil if I roast veg in the air fryer but SIL just does a quick spritz with low calorie oil spray and hers come out fine. Add chilli and garlic for stronger flavours.
Peppers roasted over open flame with no additional oil add a lovely smokey flavour, enjoyed on their own or chop them and add to a salad made with tomatoes and parsley and salt. A little sprinkle of sherry or red wine vinegar would be even better, but if you're that strict on calories, you might not be able to use it.
Whole garlic bulbs can be roasted without oil and the garlic squeezed out as a paste and mixed with other veg or into dressing like the ones I mentioned above for extra flavour.