Learn Turkish: Siz her sabah tost yersiniz. - You eat a toasted sandwich every morning.

In Turkish, tost usually refers to a hot, pressed sandwich made in a sandwich maker, rather than a plain slice of toasted bread. If you want a piece of toasted bread to put butter on, you would ask for kızarmış ekmek.

What is the "-r-" doing in the middle of the verb yersiniz?

The -r- forms the simple present tense (sometimes called the aorist tense), which is used to talk about habits and routines. Since the verb root ye- (to eat) ends in a vowel, we just add -r before attaching the personal ending -siniz (you).

Since it happens every morning, could I also use the continuous tense and say yiyorsunuz?

Yes! While the simple present tense yersiniz is the traditional grammatical choice for a repeated habit like her sabah (every morning), in everyday spoken Turkish it is extremely common to use the present continuous tense yiyorsunuz for daily routines as well.

Does Siz mean I am talking to more than one person here?

It could be, but not necessarily. Siz and the matching verb ending -siniz can mean "you" plural (talking to two or more people), but it is also used as the formal "you" when addressing a single person politely.