Winter Peas,
@Hal ? My spring peas (& broadbeans) burned up in record heat, last June.
@Gardening with Rabbits , I do that "little clump" planting with leaf lettuce. Prefer to harvest all together by pulling but can leave a small plant by cutting. I can only imagine that onions would entangle roots like crazy but don't know.
Remember this transplanting mantra: Many roots; Some leaves; One stem.
Onions are monocots like corn and, their lily cousins so the "stem" isn't so obvious as with dicots. Many roots, some leaves, one stem.
You can damage a leaf. Break the stem with my clumsy digitS' and I have killed the plant. With tiny dicot seedlings, I try not to even
touch the stem.
Onion roots are many! You can cut them off with scissors. It shouldn't set them back much.
I hold the seedling between the index and middle finger, not between the index finger and the thumb.
The soil is as soft as I can get it. I
scratch the seedling in. Yes, just hold the seedling loosely and scratch with those two digitS', leaving the seedling behind in the soil. Wear latex or nitrile gloves. Heavier gloves will hold up better but you will lose some sensitivity.
They don't really go in rows. Scratch, scratch, scratch ... Onion, onion, onion ....

Steve