During the week I usually eat out instead of cooking for myself.
During the week I don’t cook at home, I just eat out.
平日はMonday to Fridayけれど”during the week”の方が良いです。
平日仕事してます - I work during the week
平日は外食です - I eat out during the week
外食は”eat out” - eat outside —> eat out
殆ど - mostly, usually
I usually eat out, I most eat out
自炊は”cooking for yourself”けれど外食の話があるから”cook at home”も言える。cook At home は家で料理するです。
I don’t cook at home
I don’t cook for myself
イギリス 
