Anything you cook with fresh vegetables and fruits is probably going to be a decent choice. Simple lentils with rice and a roasted veggie was a pretty easy one for a while. Other than that, we mostly made foods similar to what we normally eat, but with strong flavors dialed down a little.

For your spaghetti example, maybe try something like a lentil Bolognese to increase the fiber content:

https://minimalistbaker.com/vegan-bolognese-with-mushrooms-red-lentils/

Maybe this is a point where you might want to think about developing your cooking skills? Cooking for a young child might get a bit easier when you have confidence cooking for yourself!

We had a period where she'd eat nearly anything we put in front of her but there was definitely a shift to being more picky with foods around age 3 or so. Still working through how some foods are great "sometimes foods" and making sure we're letting the little one have some part in weekly meal planning, but that's just how things can be.