14. STOCK-BASED COMPENSATION (Details Narrative) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Nov. 30, 2020	Nov. 30, 2019	Nov. 30, 2020	Nov. 30, 2019
Stock-based compensation costs capitalized as part of inventory	$ 0	$ 0	$ 0	$ 0
Intrinsic value of options exercised	3	50	$ 95	$ 67
Weighted average remaining contractual life of the options exercisable and expected to be exercisable			3 years 11 months 5 days	3 years 11 months 5 days
Stock Option and RSU Transactions
Stock-based compensation expense related to stock options and RSUs	$ 238	$ 163	$ 483	$ 313
Restricted stock units granted (in thousands)	0	0	161	0
Market value on the date of the grant			$ 1.86
Restricted stock units vested (in thousands)	11	3	14	7
Restricted stock units unvested (in thousands)	155	16	155	16
Restricted stock units unvested intrinsic value	$ 256	$ 31	$ 256	$ 31
Stock Option and RSU Transactions | Board of Directors
Restricted stock units granted (in thousands)	57	0	92	0
Market value on the date of the grant	$ 1.34		$ 1.54
2016 Equity Incentive Plan
Unrecognized stock-based compensation	$ 1,331		$ 1,331
Estimated forfeitures of unvested stock based awards, amount	3		$ 3
Weighted average period for recognition of costs			2 years 9 months 18 days
Employee Stock Purchase Plan
Weighted average period for recognition of costs			1 year
Stock-based compensation related to the ESPP	19	$ 42	$ 44	$ 91
Compensation cost related to purchase rights under the ESPP but not yet recognized	$ 41		$ 41
ESPP purchase right granted (in thousands)	72	38	72	38
ESPP shares issued (in thousands)	72	71	72	71
ESPP shares available for issuance (in thousands)	161	299	161	299