I would like to make crab cakes that call for green onions but I am out. What can I substitute for two finely chopped green onions? Would minced onion work?
In general, shallots, leeks, or chives would be milder than regular onions and probably a closer approximation to green onions, though all are usually harder to find than green onions. Leeks and chives have the advantage that they also have a similar color to green onions. The sharpness of all of these substitutes (onions included) can be tamed by cooking, but this would affect both texture and color as well. In crab cakes, the color probably matters less than the flavor, but you could mix cooked shallots or onions with raw leeks or chives to get both color and flavor.
Onion would work, but it has a much sharper flavour, so you should use maybe just a quarter as much of it, depending on how much you like the taste of onion. The flavour will be slightly different than if you used green onions, but it should still be delicious.
You could try red onions. They might have a little more flavor, but should be mild enough to taste good.