Mushy peas are a food item common in the UK. The food is comprised of peas that are crushed into a paste like substance with chunks of peas still present. Mushy peas are common with fish and chips in the UK.
In the Apple TV+ series, Ted Lasso, Jamie did not like seeing Roy kiss Keeley and pointed out to Keeley that they should talk once she had finished feeding mushy peas to the old "fart" in Roy, as mushy peas are soft and easier for the older generation to eat.