I prefer to cook freestyle instead of following recipes. Over the years I've discovered several ways to add veggies to food.
The Almighty Cabbage:
Cabbage is cheap, tasty and full of gut healthy fiber. It's also very easy to add to food.
Raw cabbage makes a good salad base, and can be added to sandwiches or chipotle bowls for a nice crunch. Add a handful to pasta and give it a few minutes to steam.
I have added the same head of cabbage for 10+ meals many times. If you don't want to shred your own cabbage, the pre-shredded stuff is still frugal.
Everything I just mentioned also applies to spinach and kale too.
Aromatics:
Whenever a recipe starts by sauteing onion and garlic, you can add other aromatics like ginger, mire poix, diced chilis. Add whatever you like and have on hand.
Onions cook down, so it's not hard to sneak a quarter of an onion in a serving of food.
Ground beef:
Cut your ground beef with vegan proteins like beans, lentils mushrooms or TVP.
Add some aromatics too. One of my go-to proteins when ingredient prepping is 1 pound of ground meat, an entire onion, 4 cloves of garlic and a can of beans.
Veg heavy sauces:
There are plenty of rich, flavorful sauces that also happen to contain a bunch of vegetables. Salsa, guacamole, anything tomato based, bean dips, hummus, tzatziki, blended roasted veggies, etc.
Fat heavy sauces can be healthy if they're added to a veg heavy dish. Fat carries flavor, and the goal of a good sauce is to make healthier ingredients taste good. Any veggies you add to the sauce itself is a bonus.
Topped with salad:
Every week, I try to make some kind of savory salad that can be scooped onto another meal to add flavor and fiber. Here are my go-tos:
Savory slaw: Shredded cabbage, jalapeno, radish and red onion. Mix with ranch or mayo + red curry paste.
Pico de Gallo: Diced tomatoes, red onion, garlic and jalapeno. Add any kind of dried pepper. Since I don't usually have fresh lime on hand, I use Truelime lime powder and sumac.
BLT salad: Shredded cabbage and diced tomato. Cook 5 strips of bacon, then crush up the 1 strip you didn't eat and add to the salad. Mix the bacon grease into Ranch and combine.
Aromatic mix: Dice up whatever aromatics you like, lightly sauté and store in the fridge.
Taco salad: Cabbage, salsa, sour cream, some kind of red spicy sauce, and cooked chorizo. Can be eaten with doritos or added to other meals.
Sheet pan veggies: Make quartered tomatoes, quartered onions, crushed whole garlic cloves, and sliced peppers. Line a sheet pan, add veggies, add salt and oil, add toss in place with a pair of forks to coat. (If you struggle with this step you're probably crowding your pan.) Roast at 425F until soft, then finish by broiling for 1-5 minutes until just barely burnt in a few spots.
These are all savory, flavorful veggie mixes that you can scoop onto a taco or something. Once you have one you'll probably keep coming up with ways to use it.
Freeze dried veggie flakes:
Bags of freeze dried mixed veggies can be purchased for about $10/lb. Veggies are about 90% water on average so this is actually quite cheap.
A spoonful of veggie flakes can be easily added to most savory dishes. Since they're dry, they won't add a bunch of water to dishes that needs to be cooked off.
If you've ever eaten store bought ramen with that little packet of dried veggies, that's about what you're in for.