If you want to be on a low carb diet as a vegetarian you have to accept eating processed food, and a lot of it.
Specifically: Soy Protein Isolate, TVP (Textured Vegetable Protein - it does have carb so don't overdo it), and Seitan (Wheat Gluten), if you are not a vegan then add eggs to that - perhaps as egg whites (i.e. more processed food).
Nuts are reasonable too. Then add in a bunch of low carb vegetables (i.e. no root vegetables), and avoid fruits for the most part.
A sample breakfast: TVP soaked in egg white with some nutritional yeast for flavor, fried as an omelet.
Snack: A cup of protein shake with as little sweetener as you can manage to handle. (You would have to buy pure soy protein isolate powder and add the sweetener yourself - most places put in a ton.)
Lunch: Seitan - fried or baked, and salad (watch the dressing - most have sugar, make your own).
Dinner: Vegetable stir fry such as zucchini, mushroom, and onion plus oil for satiation.
It's easier to be a meat eater, but if you are not a picky eater it can be done.
PS. Tofu is not 1:1, it's closer to 4:1 so it can probably be used. TVP is about 2:1.
As to the sugar, I find myself using stevia a lot now. You have to experiment with it; with some foods, you really notice the taste, and it doesn't work very well as a sweetener. But in greek yoghurt, for instance, stevia tastes really nice and not at all unlike sugar.
That brings me to a second point; as a vegetarian, one of my best investments was a simple reusable yoghurt strainer. Natural yoghurt has a lot of carbs in the form of lactose, but straining it into greek-style yoghurt removes these sugars, leaving protein and fat (which you can control by choosing no/low/full fat yoghurt). Add some stevia to it, and you've got a healty breakfast, snack, and/or dessert without any carbs.
I think it should also be said that relying solely on soya protein is not the best idea. It's a complete protein, yes, but there's very little we understand about nutrition--one of the few things we do know is that variety is better. That being said, the firmer the tofu, the fewer carbs--plus it's easier to cook (fries up nicer). If you get sick of tofu, paneer is a good alternative, and easy to make as well.
Finally, chia seeds can be a useful addition. They don't have a taste (but they absorb an incredible amount of liquid, so you can soak them overnight to make pudding), but are packed with fat, protein, and fibre (approx. 32% fat / 16% protein / 35% fibre / 7% net carb by weight).
Specifically: Soy Protein Isolate, TVP (Textured Vegetable Protein - it does have carb so don't overdo it), and Seitan (Wheat Gluten), if you are not a vegan then add eggs to that - perhaps as egg whites (i.e. more processed food).
Nuts are reasonable too. Then add in a bunch of low carb vegetables (i.e. no root vegetables), and avoid fruits for the most part.
A sample breakfast: TVP soaked in egg white with some nutritional yeast for flavor, fried as an omelet.
Snack: A cup of protein shake with as little sweetener as you can manage to handle. (You would have to buy pure soy protein isolate powder and add the sweetener yourself - most places put in a ton.)
Lunch: Seitan - fried or baked, and salad (watch the dressing - most have sugar, make your own).
Dinner: Vegetable stir fry such as zucchini, mushroom, and onion plus oil for satiation.
It's easier to be a meat eater, but if you are not a picky eater it can be done.
PS. Tofu is not 1:1, it's closer to 4:1 so it can probably be used. TVP is about 2:1.