Once your into it it's really easy. I've been vegetarian for a few years and I don't know why i worried it would be hard.
Meat gives us acsess to protein, iron and vit b12 mainly. But these are easily obtained through other healthier food. Vegetarian diets are also good for loosing weight (My cheat to a slim waist xD)
Protein can be found in any beans, chip pea's and other such pulses. It's also found in dairy products. Pasta is also meant to be a good source of protein.
Iron is found in many green leafy vegetables, and pea's. Citrus fruits and tomatoes also are good to eat as they help our bodies absorb more of the iron more easily.
Vit b is found in dairy products, especially milk, but the sunshine helps us with that so time outside as well. I drink a glass of milk a day.
But if you take a look in your local supermarket, you should find many "meat substitues". I find Quorn is my favourite but there is also "Soya" and "Tofu". There can be plain bits of meat but there is also ready made meals with these ingrediants in.
I don't think one meal a week as a vegetarian would do you any harm at all though whether it was nutritious or not, but you are correct, it is a very healthy diet when balenced.
Hope this helps, and PM me if you want any other suggestions xx
Happy christmas x