So, what is a high tunnel?
A high tunnel is another name for a hoop house or a passive greenhouse. All produce is grown directly in the soil, not in pots or trays but directly in the soil. The high tunnel structure alone (even without supplemental heat) will extend the growing season. A typical growing season will start in March and end at the end of December.
Typical tillage equipment can be used inside.
Drop down curtain walls and large sliding doors on the end allow for ventilation.
Early indeterminate tomato crops can be trellised vertically.