I'd recommend taking a look at Prof Roy Taylor's stuff, including a book which came out earlier this year:
https://www.ncl.ac.uk/magres/research/diabetes/reversal/#publicinformation
This is really the best explanation I've seen for relationship between food, weight, exercise and BG, for those who have some degree of insulin resistance, as seems likely to be the case with you. Research funded by Diabetes UK and the basis for a Type 2 diabetes program being trialled by the NHS, but very applicable to people at a "pre-diabetic" stage.
You'll find a lot of people focusing narrowly on carbohydrates. This is only part of the story, but you'd probably find you get BG improvements by cutting down on carbs.
It can be difficult as a vegetarian/vegan, because you probably tend to eat quite a lot of grains, and they can be the worst culprits for increasing BG.
Personally, I'm a flexitarian - mainly plants, with a bit of fish and chicken. When I first got diagnosed with T2, it was really surprising to see how much bread etc affected my BG levels. I ended up replacing it largely with nuts and seeds. This helped a lot, but really I got rid of my T2 via weight loss, along the lines described by Taylor.
I still don't eat much bread (a half slice of pumpernickel now and then), but these days it's largely a matter of habit - I've grown to really like nuts & seeds!
Anyway, maybe a 3-pronged approach is worth looking at:
- Work out via testing which carbs do what to you, and adjust portion sizes.
- Lose some weight. Unless you're already underweight, the chances are this would be good for your BG and general health. Doesn't matter whether or not you're officially "overweight".
- Moderate exercise. Helps with weight loss, helps reduce insulin resistance, good for CV health, generally the biggest risk for people with elevated BG.