Here is Dr B on tomatoes:
"Tomatoes, tomato paste, and tomato sauce
Tomatoes, as you know, are actually a fruit, not a vegetable, and as with citrus fruits, their tang can conceal just how sweet they are. The prolonged cooking necessary for the preparation of tomato sauces releases a lot of glucose, and you would do well to avoid them. If you’re at someone’s home for dinner and are served meat or fish covered with tomato sauce, just scrape it off. The small amount that might remain should not significantly affect your blood sugar. If you are having them uncooked in salad, limit yourself to one slice or a single cherry tomato per cup of salad. (See page 380 for a recipe for a low-carbohydrate, tomato-free, Italian-style red sauce that can be good over, say, a broiled, sautéed, or grilled chicken breast or veal scallopine.) Onions fall into this same category—despite some sharp flavor, they’re quite sweet, some varieties sweeter than others. There are other vegetables in the allium family that can be easily substituted, although in smaller quantities, such as shallots and elephant garlic."
I realise everyone will make their own decisions, but if bg is raised after a meal including tomatoes and/or onions IMO they might well be the culprits.