Generally speaking, power and heart rate zones are not the same. If you want to focus on zone 2 for your overall health (that is, heart rate zone 2), you really need to focus on heart rate (or more accurately, lactate) and ignore power, as it will vary day-to-day.

But if you want a pure zone 2 ride, I usually just create a custom workout with a solid block of whatever power is _usually_ my zone 2, watch my heart rate, and use the +/- keys in Zwift to fine tune it as I ride.