Tips for gaining weight?

eat slightly more than that amount every day , eat about 500 extra calories per day to your diet.

You may look into doing your own french fries with the air fryer.
Snack on good fats like beans, nuts, seeds , peanut butter, almond butter, hummus, avocados
Opt in for soy based protein shakes like nutrilite, make your own smoothies + plain greek yogurt.
If you like salads you can add in easy calories through olive oil/nut oil, seeds, fruits, nuts, tofu , bread , cheese ,sour cream, potatoes, omelete
Don't forget about your protein because you're a vegetarian, you need your protein sources from soy & quinoa / beans /nuts /seeds.
sesame seeds,pumpkin seeds, pistachio,almond,walnuts are really good.
Eat calorie and protein-rich foods like beans, nuts, peanut and almond butters, soy products, small meals throughout the day.
Eat your eggs and dairy , milk/yogurt , grass fed butter, cheese.

snack frequently on nuts if your tummy can take it, preferably add in a supper, that makes 6 meals a day

Hope this helps.

Patience with gaining is the hardest for me. I have to eat what seems like constantly to reach my calorie goals every day (and I hate unhealthy, heavy foods so cheating in calories is impossible). Beans and legumes in wraps are big in my diet when I'm not being lazy about it, and so is pizza (because I make/sell pizza things).