Our go-to is a sandwich of turkey breast (lowest sodium avail) on 60cal ea wheat bread. I add an apple and some baby carrots. This is about 300cal, or 3WW points.

Easy-to-make means either a cold salad or reheating some leftovers.
Here's one I do that gives leftovers:
1 can diced tomatoes (I prefer to use versions with flavor, such as fire-roasted, garlic, or green pepper)
1 can corn kernels, drained
1 can beans, drained and rinsed (my favorite is actually lentil soup)
Put 'em all in a pot, add black pepper maybe a bit of salt, and cook for 10 minutes.
Makes several meals, add a little something different to prevent boredom, such as precooked meat, another vegetable, or just some interesting spices.
My favorite is to add half a diced avocado and some cilantro.
Around 250 calories without the add-ins if divided into thirds, but adjust the amount you serve to fit target.

Some type of protein for lunch today was two slices of cure 81 ham each with a slice of sliced sharp cheddar cheese. Other days maybe a green salad sometimes a can of chicken mixed with some mayo. I won't go there when I'm misbehaving.