I've had them served to me 2 different ways.
Both were simply green peas in a standard white sauce. One way the peas were whole and the dish included boiled pearl onions (probably canned). The other way, the peas were mashed.
So ask him which version he likes.
I'm not a green pea fan, but I like the peas and pearl onions in cream sauce. For Thanksgiving, I'd make my white sauce with real butter and perhaps half and half or, at a minimum, whole milk.
Or, take a look in the freezer section. Green Giant used to make a creamed peas and pearl onions in a boiling bag. Maybe they still do and that might be a reasonable solution if only one person wants creamed peas. It's not like you don't have a ton of other cooking to do at Thanksgiving.