Can green tomatoes be used as substitute for tomatillos?

tomatillos and tomatoes are very different , they are not related so would not necessarily work the same way. They are tarter than tomatoes. I did't think green tomatoes really tasted like anything.

I have not, but I used to raise tomatillos and the only remotely similar experience with abundance came from a friend who once lived in Northern Minnesota during smelt season. But that's another story.

Tomatillos are, of course smaller than tomatoes of any color. They are also significantly lower in moisture. To sub green tomatoes, I'd suggest first coring and quartering them. Then use your thumbs to gently scrape out the seed pockets, where a lot of water is stored. Afterwards, roughly chop the tomatoes and toss them with some salt (how much will depend on how many tomatoes you have, but start with a teaspoon) in a colander and let them drain for about a half hour. Last, dump them out on a clean kitchen towel (because yesterday was Climate Change Day, and we're pledging to go zero-waste, right?) and blot them dry. Go ahead with your salsa, and by all means please let us know how it turns out. I suspect you're on to something beyond fried green tomatoes.