Q. English muffins are typically eaten after toasting them, does toasting make them pas Yisroel?

A. Shulchan Aruch (Y.D. 112: 12) quotes two opinions whether bread that was fully baked and is then further baked or toasted to improve taste, if that second introduction in the oven turns it into Pas Yisroel or not. It seems that he sides with the opinion that it does not. See also Aruch Hashulchan (ibid.)
Horav Shlomo Miller’s Shlit’a opinion is that since the English muffins are fully baked when they are sold, toasting them, even if it enhances markedly their flavor, does not turn them into Pas Yisroel.
He pointed out Igrois Moishe’s (Y.D. 3:24 and 1: 57-58) ruling in regards to the exemption of tevila for a toaster, since it does not actually bake the bread, just betters it.

Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit”a.