Q. I have heard that if a piece of matzah is broken and I place it into the oven to bake further until the broken edge browns, that this piece has the status of a Shaleim and can be used as one of the Lechem Mishnah.

Assuming this to be correct, can a well-toasted slice of bread be considered a Shaleim and how browned must it have become?

A. It has become an accepted practice to re-bake or flame the edge of a broken matza to turn it into a shleimo (Seder Haoruch 22,4 – Maadaney Yom Tov ch. 122 – Palgey Mayim 21 – Sidur Pesach Kehilchoso p. 22).
Poiskim disagree as to how much of the matza should be missing to make this necessary, also if the roundness of the matza has to be restored and if it can be done on Yom Tov (Shaarey Teshuva 274,1 – Maadaney Yom Tov ibid.).
Horav Shlomo Miller’s Shlit’a opinion is that the above does not apply to turning a slice of toast into a complete “sholem” bread, as after all, it would be recognized by all as only a well browned slice of bread.

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