Good advice above but also know that a lot of dietitians (as well as most doctors) are not completely educated on a vegetarian/vegan diet. .
Here in Canada, at least, all registered dietitians are very well versed in vegetarian diets. It is part of our training! We learn about healthy vegetarian diets, and how to modify vegetarian diets for individuals with various health conditions, including heart disease and diabetes. We also have training in cultural food practices, so that we can counsel clients who are vegetarian for cultural or religious reasons.
Maybe it is different in different countries, or maybe there are some old-school dietitians out there who haven't updated their knowledge of vegetarian diets since they went through school, but any current, Canadian, registered dietitian is going to have a lot of knowledge about vegetarian and vegan diets.
You can eat a vegetarian or vegan diet and still be eating a very unhealthy diet (I've counselled some individuals with vegetarian diets that consisted only of white bread, carrots, peas, and potatoes, believe it or not! Not very healthy!) But, of course, vegetarian and vegan diets, if done right, can be very healthy!
Myself, I am mostly vegetarian, although I could be described more as a pescetarian - I like the occasional piece of fish, especially salmon. Although I can get my healthy omega-3s from plenty of vegetarian sources, I do like fish. I also enjoy dairy, mostly in the form of yogourt, which is a staple in my diet. I've never been a fan of liquid milk, not even as a child, but you'll pry my yogourt from my cold, dead hands!

I also enjoy some cheese - such as in a vegetarian lasagna, made with whole wheat noodles, of course!
I love legumes (mostly beans and lentils - I'm not a pea fan), vegetables, fruit, and whole grains like quinoa. I love quinoa - it's a complete protein and has plenty of fibre. I'm allergic to soy and nuts, so I can't include those in my diet, but I know many vegetarians have those as dietary staples. I love using lentils in places you wouldn't think to find them - muffins, smoothies, etc. And I love a good black bean brownie for a dessert when I'm being decadent.
Some resources for great vegetarian or vegan recipes:
https://ohsheglows.com/ (although I modify a number of her recipes due to the soy or nuts in them)
https://www.lentils.ca/ (I have several of their recipe books and I love them!)
https://www.halfyourplate.ca/
https://www.cookspiration.com/genre.aspx?g=25
https://www.cookspiration.com/genre.aspx?g=23
https://www.eatrightontario.ca/en/Recipes/Vegetarian.aspx
I also make my own "energy bites" to eat before workouts, instead of buying processed bars. I use this recipe with some modifications:
https://smashedpeasandcarrots.com/no-bake-energy-bites-recipe/
I can't do nut butters, so I use sunflower seed butter. Instead of coconut flakes (I don't like the taste of coconut), I use wheat germ, chia seed, or hemp hearts. Or just more flaxseed, depending on what I have in the cupboards and fridge. It's a great, versatile recipe. Instead of mini chocolate chips, I'll sometimes used some dried fruit pieces, like raisins, dried cranberries, or other small chopped pieces of dried fruit.
And while the recipes aren't all vegetarian, The Sneaky Chef:
https://www.thesneakychef.com/ has some great ways of including more vegetables in your diet (especially children's diets, hence the name The Sneaky Chef).