Orach is similar to spinach - very nearly as tender and just a surprisingly nice veggie. Lambs quarters is a related weed but quite a bit tougher.
Orach can, however, get stemmy fairly quickly and doesn't develop a very large rosette of leaves. That means you need to sit down on your garden stool and pick it when it's quite small. If it's the volunteers, they will really need to be
thinned hard! If you are doing any transplanting, you'll need to be in there with your spoon or popsicle stick or whatever you use and
move 'em early.
And, early can be a problem. They literally show up before I do in the Spring. It must take very little heat to start 'em growing. That means you can start your harvesting before you are even thinking about such activities . . . and before there's anything to go with 'em. Which is a little sad in the salad department.
You know, I've
always messed up with remembering that
spinach will overwinter.

Never have I gotten spinach seed in the ground during September (I guess it would be) so that I could have an early harvest. Since orach self-seeds so enthusiastically and tastes so much like spinach - it saves me from my failings, somewhat.
Pigweed is a little tricky to harvest at a good stage - like dandelions that way. No flower, tho' . . . if there's a hint of bolting, you've waited too long. The best weed will be in good soil, of course.

You know, absolutely where you
don't want it!! So, does that mean you've got to tolerate a weed where you don't want it to grow just so you can harvest a pot of greens??

Well, maybe.
What I like to do is find it outside the garden. The neighbor beside my smaller veggie garden lets lots and LOTS of weeds grow. :/ If they've gotten sufficient rain, there's usually a batch over there where I can almost stand on my side of the line and pull enuf pigweed on his side to fill a bag. Then hide any evidence of my trespass and head for the kitchen!!
Steve